diff --git a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/bar/bar.js b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/bar/bar.js
index 2101b6c9d7..a2ea94ca9e 100644
--- a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/bar/bar.js	
+++ b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/bar/bar.js	
@@ -5,4 +5,4 @@ function _classCallCheck(instance, Constructor) { if (!(instance instanceof Cons
 var Test = function Test() {
   _classCallCheck(this, Test);
 };
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIi4uLy4uL3NyYy9iYXIvYmFyLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiI7Ozs7SUFBTSIsImZpbGUiOiJiYXIuanMiLCJzb3VyY2VzQ29udGVudCI6WyJjbGFzcyBUZXN0IHtcblxufSJdfQ==
+//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIi4uLy4uL3NyYy9iYXIvYmFyLmpzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiI7Ozs7SUFBTSxJIiwiZmlsZSI6ImJhci5qcyIsInNvdXJjZXNDb250ZW50IjpbImNsYXNzIFRlc3Qge1xuXG59Il19
diff --git a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/foo.js b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/foo.js
index d9c86c7221..0a833dbc8b 100644
--- a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/foo.js	
+++ b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps inline/out-files/lib/foo.js	
@@ -3,4 +3,4 @@
 arr.map(function (x) {
   return x * MULTIPLIER;
 });
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIi4uL3NyYy9mb28uanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6Ijs7QUFBQSxJQUFJLEdBQUosQ0FBUTtTQUFLLElBQUksVUFBSjtDQUFMLENBQVIiLCJmaWxlIjoiZm9vLmpzIiwic291cmNlc0NvbnRlbnQiOlsiYXJyLm1hcCh4ID0+IHggKiBNVUxUSVBMSUVSKTsiXX0=
+//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIi4uL3NyYy9mb28uanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6Ijs7QUFBQSxJQUFJLEdBQUosQ0FBUTtBQUFBLFNBQUssSUFBSSxVQUFUO0FBQUEsQ0FBUiIsImZpbGUiOiJmb28uanMiLCJzb3VyY2VzQ29udGVudCI6WyJhcnIubWFwKHggPT4geCAqIE1VTFRJUExJRVIpOyJdfQ==
diff --git a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/bar/bar.js.map b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/bar/bar.js.map
index e44ef77215..19eab2f949 100644
--- a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/bar/bar.js.map	
+++ b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/bar/bar.js.map	
@@ -1 +1 @@
-{"version":3,"sources":["../../src/bar/bar.js"],"names":[],"mappings":";;;;IAAM","file":"bar.js","sourcesContent":["class Test {\n\n}"]}
\ No newline at end of file
+{"version":3,"sources":["../../src/bar/bar.js"],"names":[],"mappings":";;;;IAAM,I","file":"bar.js","sourcesContent":["class Test {\n\n}"]}
diff --git a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/foo.js.map b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/foo.js.map
index 96682885b2..b8d69ed4f8 100644
--- a/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/foo.js.map	
+++ b/packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/foo.js.map	
@@ -1 +1 @@
-{"version":3,"sources":["../src/foo.js"],"names":[],"mappings":";;AAAA,IAAI,GAAJ,CAAQ;SAAK,IAAI,UAAJ;CAAL,CAAR","file":"foo.js","sourcesContent":["arr.map(x => x * MULTIPLIER);"]}
\ No newline at end of file
+{"version":3,"sources":["../src/foo.js"],"names":[],"mappings":";;AAAA,IAAI,GAAJ,CAAQ;AAAA,SAAK,IAAI,UAAT;AAAA,CAAR","file":"foo.js","sourcesContent":["arr.map(x => x * MULTIPLIER);"]}
diff --git a/packages/babel-cli/test/fixtures/babel/filename --out-file --source-maps inline/out-files/script2.js b/packages/babel-cli/test/fixtures/babel/filename --out-file --source-maps inline/out-files/script2.js
index 7e591ab7bb..58c2fc63b2 100644
--- a/packages/babel-cli/test/fixtures/babel/filename --out-file --source-maps inline/out-files/script2.js	
+++ b/packages/babel-cli/test/fixtures/babel/filename --out-file --source-maps inline/out-files/script2.js	
@@ -4,4 +4,4 @@ arr.map(function (x) {
   return x * MULTIPLIER;
 });
 
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNjcmlwdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiOztBQUFBLElBQUksR0FBSixDQUFRO1NBQUssSUFBSSxVQUFKO0NBQUwsQ0FBUiIsImZpbGUiOiJzY3JpcHQyLmpzIiwic291cmNlc0NvbnRlbnQiOlsiYXJyLm1hcCh4ID0+IHggKiBNVUxUSVBMSUVSKTsiXX0=
+//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNjcmlwdC5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiOztBQUFBLElBQUksR0FBSixDQUFRO0FBQUEsU0FBSyxJQUFJLFVBQVQ7QUFBQSxDQUFSIiwiZmlsZSI6InNjcmlwdDIuanMiLCJzb3VyY2VzQ29udGVudCI6WyJhcnIubWFwKHggPT4geCAqIE1VTFRJUExJRVIpOyJdfQ==
diff --git a/packages/babel-cli/test/fixtures/babel/filename-sourcemap --out-file --source-maps inline/out-files/script2.js b/packages/babel-cli/test/fixtures/babel/filename-sourcemap --out-file --source-maps inline/out-files/script2.js
index 15cc7b65d8..891ae37a81 100644
--- a/packages/babel-cli/test/fixtures/babel/filename-sourcemap --out-file --source-maps inline/out-files/script2.js	
+++ b/packages/babel-cli/test/fixtures/babel/filename-sourcemap --out-file --source-maps inline/out-files/script2.js	
@@ -4,4 +4,4 @@ var foo = function foo() {
   return 4;
 };
 
-//# sourceMappingURL=data:application/json;base64,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
+//# sourceMappingURL=data:application/json;base64,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
diff --git a/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps inline/out-files/script3.js b/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps inline/out-files/script3.js
index c1fc202b90..cd0326f68f 100644
--- a/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps inline/out-files/script3.js	
+++ b/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps inline/out-files/script3.js	
@@ -11,4 +11,4 @@ arr.map(function (x) {
   return x * MULTIPLIER;
 });
 
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNjcmlwdC5qcyIsInNjcmlwdDIuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6Ijs7OztJQUFNOzs7Ozs7QUNBTixJQUFJLEdBQUosQ0FBUTtTQUFLLElBQUksVUFBSjtDQUFMLENBQVIiLCJmaWxlIjoic2NyaXB0My5qcyIsInNvdXJjZXNDb250ZW50IjpbImNsYXNzIFRlc3Qge1xuXG59IiwiYXJyLm1hcCh4ID0+IHggKiBNVUxUSVBMSUVSKTsiXX0=
+//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNjcmlwdC5qcyIsInNjcmlwdDIuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6Ijs7OztJQUFNLEk7Ozs7OztBQ0FOLElBQUksR0FBSixDQUFRO0FBQUEsU0FBSyxJQUFJLFVBQVQ7QUFBQSxDQUFSIiwiZmlsZSI6InNjcmlwdDMuanMiLCJzb3VyY2VzQ29udGVudCI6WyJjbGFzcyBUZXN0IHtcblxufSIsImFyci5tYXAoeCA9PiB4ICogTVVMVElQTElFUik7Il19
diff --git a/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps/out-files/script3.js.map b/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps/out-files/script3.js.map
index 4443440920..6dc6dd4027 100644
--- a/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps/out-files/script3.js.map	
+++ b/packages/babel-cli/test/fixtures/babel/filenames --out-file --source-maps/out-files/script3.js.map	
@@ -1 +1 @@
-{"version":3,"sources":["script.js","script2.js"],"names":[],"mappings":";;;;IAAM;;;;;;ACAN,IAAI,GAAJ,CAAQ;SAAK,IAAI,UAAJ;CAAL,CAAR","file":"script3.js","sourcesContent":["class Test {\n\n}","arr.map(x => x * MULTIPLIER);"]}
\ No newline at end of file
+{"version":3,"sources":["script.js","script2.js"],"names":[],"mappings":";;;;IAAM,I;;;;;;ACAN,IAAI,GAAJ,CAAQ;AAAA,SAAK,IAAI,UAAT;AAAA,CAAR","file":"script3.js","sourcesContent":["class Test {\n\n}","arr.map(x => x * MULTIPLIER);"]}
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/full/source-map.json b/packages/babel-core/test/fixtures/transformation/source-maps/full/source-map.json
index 35d93706a8..cf4f823e4a 100644
--- a/packages/babel-core/test/fixtures/transformation/source-maps/full/source-map.json
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/full/source-map.json
@@ -3,6 +3,6 @@
   "file": "source-maps/full/expected.js",
   "sources": ["source-maps/full/actual.js"],
   "names": [],
-  "mappings": "AAAA,IAAI,GAAJ,CAAQ;SAAK,IAAI,CAAJ;CAAL,CAAR",
+  "mappings": "AAAA,IAAI,GAAJ,CAAQ;AAAA,SAAK,IAAI,CAAT;AAAA,CAAR",
   "sourcesContent": ["arr.map(x => x * x);"]
 }
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js b/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
index 6e490e6707..5e0d972ab0 100644
--- a/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/inline/expected.js
@@ -1,4 +1,4 @@
 arr.map(function (x) {
   return x * x;
 });
-//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXBzL2lubGluZS9hY3R1YWwuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBQUEsSUFBSSxHQUFKLENBQVE7U0FBSyxJQUFJLENBQUo7Q0FBTCxDQUFSIiwiZmlsZSI6InNvdXJjZS1tYXBzL2lubGluZS9leHBlY3RlZC5qcyIsInNvdXJjZXNDb250ZW50IjpbImFyci5tYXAoeCA9PiB4ICogeCk7Il19
+//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInNvdXJjZS1tYXBzL2lubGluZS9hY3R1YWwuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBQUEsSUFBSSxHQUFKLENBQVE7QUFBQSxTQUFLLElBQUksQ0FBVDtBQUFBLENBQVIiLCJmaWxlIjoic291cmNlLW1hcHMvaW5saW5lL2V4cGVjdGVkLmpzIiwic291cmNlc0NvbnRlbnQiOlsiYXJyLm1hcCh4ID0+IHggKiB4KTsiXX0=
diff --git a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map/source-map.json b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map/source-map.json
index ba7a5c1760..be097b621d 100644
--- a/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map/source-map.json
+++ b/packages/babel-core/test/fixtures/transformation/source-maps/input-source-map/source-map.json
@@ -1,6 +1,6 @@
 {
   "version": 3,
-  "mappings": "AAAA;SAAgB,A,AAAC,E;CAAP",
+  "mappings": "AAAA,UAAU;SAAM,A,AAAC;A",
   "names": [],
   "sources": [
     "original.js"
diff --git a/packages/babel-generator/src/buffer.js b/packages/babel-generator/src/buffer.js
index 1d31e4faef..5a3d3b2f27 100644
--- a/packages/babel-generator/src/buffer.js
+++ b/packages/babel-generator/src/buffer.js
@@ -19,6 +19,13 @@ export default class Buffer {
     // to make sure that v8 doesn't "flatten" the string more often than needed
     // see https://github.com/babel/babel/pull/3283 for details.
     this.last = "";
+
+    this.map = null;
+    this._sourcePosition = {
+      line: null,
+      column: null,
+      filename: null,
+    };
   }
 
   printedCommentStarts: Object;
@@ -230,6 +237,40 @@ export default class Buffer {
     }
   }
 
+  /**
+   * Sets a given position as the current source location so generated code after this call
+   * will be given this position in the sourcemap.
+   */
+
+  source(prop: string, loc: Location) {
+    if (prop && !loc) return;
+
+    let pos = loc ? loc[prop] : null;
+
+    this._sourcePosition.line = pos ? pos.line : null;
+    this._sourcePosition.column = pos ? pos.column : null;
+    this._sourcePosition.filename = loc && loc.filename || null;
+  }
+
+  /**
+   * Call a callback with a specific source location and restore on completion.
+   */
+
+  withSource(prop: string, loc: Location, cb: () => void) {
+    // Use the call stack to manage a stack of "source location" data.
+    let originalLine = this._sourcePosition.line;
+    let originalColumn = this._sourcePosition.column;
+    let originalFilename = this._sourcePosition.filename;
+
+    this.source(prop, loc);
+
+    cb();
+
+    this._sourcePosition.line = originalLine;
+    this._sourcePosition.column = originalColumn;
+    this._sourcePosition.filename = originalFilename;
+  }
+
   /**
    * Push a string to the buffer, maintaining indentation and newlines.
    */
@@ -276,6 +317,9 @@ export default class Buffer {
       }
     }
 
+    // If there the line is ending, adding a new mapping marker is redundant
+    if (str[0] !== "\n") this.map.mark(this._sourcePosition);
+
     //
     this.position.push(str);
     this.buf += str;
diff --git a/packages/babel-generator/src/printer.js b/packages/babel-generator/src/printer.js
index a8c843d82c..5ae1adf9ad 100644
--- a/packages/babel-generator/src/printer.js
+++ b/packages/babel-generator/src/printer.js
@@ -51,9 +51,10 @@ export default class Printer extends Buffer {
 
     if (opts.before) opts.before();
 
-    this.map.mark(node);
-
-    this._print(node, parent);
+    let loc = (t.isProgram(node) || t.isFile(node)) ? null : node.loc;
+    this.withSource("start", loc, () => {
+      this._print(node, parent);
+    });
 
     // Check again if any of our children may have left an aux comment on the stack
     if (node.loc) this.printAuxAfterComment();
@@ -64,7 +65,6 @@ export default class Printer extends Buffer {
 
     // end
     this._printStack.pop();
-    if (parent) this.map.mark(parent);
     if (opts.after) opts.after();
 
     this.format.concise = oldConcise;
@@ -268,46 +268,50 @@ export default class Printer extends Buffer {
       this.printedCommentStarts[comment.start] = true;
     }
 
-    this.catchUp(comment);
+    // Exclude comments from source mappings since they will only clutter things.
+    this.withSource(null, null, () => {
+      this.catchUp(comment);
 
-    // whitespace before
-    this.newline(this.whitespace.getNewlinesBefore(comment));
+      // whitespace before
+      this.newline(this.whitespace.getNewlinesBefore(comment));
 
-    let column = this.position.column;
-    let val    = this.generateComment(comment);
+      let column = this.position.column;
+      let val    = this.generateComment(comment);
 
-    if (column && !this.isLast(["\n", " ", "[", "{"])) {
-      this._push(" ");
-      column++;
-    }
-
-    //
-    if (comment.type === "CommentBlock" && this.format.indent.adjustMultilineComment) {
-      let offset = comment.loc && comment.loc.start.column;
-      if (offset) {
-        let newlineRegex = new RegExp("\\n\\s{1," + offset + "}", "g");
-        val = val.replace(newlineRegex, "\n");
+      if (column && !this.isLast(["\n", " ", "[", "{"])) {
+        this._push(" ");
+        column++;
       }
 
-      let indent = Math.max(this.indentSize(), column);
-      val = val.replace(/\n/g, `\n${repeating(" ", indent)}`);
-    }
+      //
+      if (comment.type === "CommentBlock" && this.format.indent.adjustMultilineComment) {
+        let offset = comment.loc && comment.loc.start.column;
+        if (offset) {
+          let newlineRegex = new RegExp("\\n\\s{1," + offset + "}", "g");
+          val = val.replace(newlineRegex, "\n");
+        }
 
-    if (column === 0) {
-      val = this.getIndent() + val;
-    }
+        let indent = Math.max(this.indentSize(), column);
+        val = val.replace(/\n/g, `\n${repeating(" ", indent)}`);
+      }
 
-    // force a newline for line comments when retainLines is set in case the next printed node
-    // doesn't catch up
-    if ((this.format.compact || this.format.concise || this.format.retainLines) && comment.type === "CommentLine") {
-      val += "\n";
-    }
+      if (column === 0) {
+        val = this.getIndent() + val;
+      }
 
-    //
-    this._push(val);
+      // force a newline for line comments when retainLines is set in case the next printed node
+      // doesn't catch up
+      if ((this.format.compact || this.format.concise || this.format.retainLines) &&
+          comment.type === "CommentLine") {
+        val += "\n";
+      }
 
-    // whitespace after
-    this.newline(this.whitespace.getNewlinesAfter(comment));
+      //
+      this._push(val);
+
+      // whitespace after
+      this.newline(this.whitespace.getNewlinesAfter(comment));
+    });
   }
 
   printComments(comments?: Array<Object>) {
diff --git a/packages/babel-generator/src/source-map.js b/packages/babel-generator/src/source-map.js
index beea55bddf..ca23337e7e 100644
--- a/packages/babel-generator/src/source-map.js
+++ b/packages/babel-generator/src/source-map.js
@@ -1,5 +1,4 @@
 import sourceMap from "source-map";
-import * as t from "babel-types";
 
 /**
  * Build a sourcemap.
@@ -43,46 +42,40 @@ export default class SourceMap {
   }
 
   /**
-   * Mark a node's generated position, and add it to the sourcemap.
+   * Mark the current generated position with a source position. May also be passed null line/column
+   * values to insert a mapping to nothing.
    */
 
-  mark(node) {
-    let loc = node.loc;
-    if (!loc) return; // no location info
-
+  mark(sourcePos: Object) {
     let map = this.map;
     if (!map) return; // no source map
 
-    if (t.isProgram(node) || t.isFile(node)) return; // illegal mapping nodes
-
     let position = this.position;
 
-    let generated = {
-      line: position.line,
-      column: position.column
-    };
+    // Adding an empty mapping at the start of a generated line just clutters the map.
+    if (this._lastGenLine !== position.line && sourcePos.line === null) return;
 
-    let original = loc.start;
-
-    // Avoid emitting duplicates on either side. Duplicated
-    // original values creates unnecesssarily large source maps
-    // and increases compile time. Duplicates on the generated
-    // side can lead to incorrect mappings.
-    if (comparePosition(original, this.last.original)
-        || comparePosition(generated, this.last.generated)) {
+    // If this mapping points to the same source location as the last one, we can ignore it since
+    // the previous one covers it.
+    if (this._lastGenLine === position.line && this._lastSourceLine === sourcePos.line &&
+      this._lastSourceColumn === sourcePos.column) {
       return;
     }
 
-    this.last = {
-      source: loc.filename || this.opts.sourceFileName,
-      generated: generated,
-      original: original
-    };
+    this._lastGenLine = position.line;
+    this._lastSourceLine = sourcePos.line;
+    this._lastSourceColumn = sourcePos.column;
 
-    map.addMapping(this.last);
+    map.addMapping({
+      generated: {
+        line: position.line,
+        column: position.column
+      },
+      source: sourcePos.line == null ? null : sourcePos.filename || this.opts.sourceFileName,
+      original: sourcePos.line == null ? null : {
+        line: sourcePos.line,
+        column: sourcePos.column,
+      },
+    });
   }
 }
-
-function comparePosition(a, b) {
-  return a.line === b.line &&  a.column === b.column;
-}
diff --git a/packages/babel-generator/test/index.js b/packages/babel-generator/test/index.js
index 7ee494b75d..23820dd7d7 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -43,7 +43,7 @@ suite("generation", function () {
       version: 3,
       sources: [ 'a.js', 'b.js' ],
       names: [],
-      mappings: 'AAAA,SAAS,EAAT,CAAa,GAAb,EAAkB;AAAE,UAAQ,GAAR,CAAY,GAAZ,EAAF;CAAlB;;GCAG,OAAH',
+      mappings: 'AAAA,SAAS,EAAT,CAAa,GAAb,EAAkB;AAAE,UAAQ,GAAR,CAAY,GAAZ;AAAF;;ACAlB,GAAG,OAAH',
       sourcesContent: [
       'function hi (msg) { console.log(msg); }\n',
         'hi(\'hello\');\n'