diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 395f64488909b..afc2a025da512 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -4372,10 +4372,10 @@ namespace ts {
         }
 
         /**
-         * Skips trivia such as comments and white-space that can optionally overriden by the source map source
+         * Skips trivia such as comments and white-space that can be optionally overridden by the source-map source
          */
         function skipSourceTrivia(source: SourceMapSource, pos: number): number {
-            return source.skipTrivia ? source.skipTrivia(pos) : skipTrivia(sourceMapSource.text, pos);
+            return source.skipTrivia ? source.skipTrivia(pos) : skipTrivia(source.text, pos);
         }
 
         /**
diff --git a/src/testRunner/unittests/customTransforms.ts b/src/testRunner/unittests/customTransforms.ts
index aef9ed745ec56..0ac1434134231 100644
--- a/src/testRunner/unittests/customTransforms.ts
+++ b/src/testRunner/unittests/customTransforms.ts
@@ -129,5 +129,34 @@ namespace ts {
             },
             { sourceMap: true }
         );
+
+        emitsCorrectly("skipTriviaExternalSourceFiles",
+            [
+                {
+                    file: "source.ts",
+                    // The source file contains preceding trivia (e.g. whitespace) to try to confuse the `skipSourceTrivia` function.
+                    text: "         original;"
+                },
+            ],
+            {
+                before: [
+                    context => node => visitNode(node, function visitor(node: Node): Node {
+                        if (isIdentifier(node) && node.text === "original") {
+                            const newNode = createIdentifier("changed");
+                            setSourceMapRange(newNode, {
+                              pos: 0,
+                              end: 7,
+                              // Do not provide a custom skipTrivia function for `source`.
+                              source: createSourceMapSource("another.html", "changed;")
+                            });
+                            return newNode;
+                        }
+                        return visitEachChild(node, visitor, context);
+                    })
+                ]
+            },
+            { sourceMap: true }
+        );
+
     });
 }
diff --git a/tests/baselines/reference/customTransforms/skipTriviaExternalSourceFiles.js b/tests/baselines/reference/customTransforms/skipTriviaExternalSourceFiles.js
new file mode 100644
index 0000000000000..8c7fecf97f0bb
--- /dev/null
+++ b/tests/baselines/reference/customTransforms/skipTriviaExternalSourceFiles.js
@@ -0,0 +1,6 @@
+// [source.js.map]
+{"version":3,"file":"source.js","sourceRoot":"","sources":["source.ts","another.html"],"names":[],"mappings":"ACAA,OAAO,CDAW"}
+
+// [source.js]
+changed;
+//# sourceMappingURL=source.js.map
\ No newline at end of file