diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index e9ccc23d6eb..42589c4228e 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -337,17 +337,14 @@ namespace ts {
         return result;
     }
 
-    export function getPositionOfLineAndCharacter(sourceFile: SourceFileLike, line: number, character: number): number {
-        return sourceFile.getPositionOfLineAndCharacter ?
-            sourceFile.getPositionOfLineAndCharacter(line, character) :
-            computePositionOfLineAndCharacter(getLineStarts(sourceFile), line, character, sourceFile.text);
-    }
-
+    export function getPositionOfLineAndCharacter(sourceFile: SourceFileLike, line: number, character: number): number;
     /* @internal */
-    export function getPositionOfLineAndCharacterWithEdits(sourceFile: SourceFileLike, line: number, character: number): number {
+    // tslint:disable-next-line:unified-signatures
+    export function getPositionOfLineAndCharacter(sourceFile: SourceFileLike, line: number, character: number, allowEdits?: true): number;
+    export function getPositionOfLineAndCharacter(sourceFile: SourceFileLike, line: number, character: number, allowEdits?: true): number {
         return sourceFile.getPositionOfLineAndCharacter ?
-            sourceFile.getPositionOfLineAndCharacter(line, character) :
-            computePositionOfLineAndCharacter(getLineStarts(sourceFile), line, character, sourceFile.text, /*allowEdits*/ true);
+            sourceFile.getPositionOfLineAndCharacter(line, character, allowEdits) :
+            computePositionOfLineAndCharacter(getLineStarts(sourceFile), line, character, sourceFile.text, allowEdits);
     }
 
     /* @internal */
diff --git a/src/compiler/sourcemap.ts b/src/compiler/sourcemap.ts
index 190cac3b761..00a78b0a93c 100644
--- a/src/compiler/sourcemap.ts
+++ b/src/compiler/sourcemap.ts
@@ -616,7 +616,7 @@ namespace ts {
 
         function processMapping(mapping: Mapping): MappedPosition {
             const generatedPosition = generatedFile !== undefined
-                ? getPositionOfLineAndCharacterWithEdits(generatedFile, mapping.generatedLine, mapping.generatedCharacter)
+                ? getPositionOfLineAndCharacter(generatedFile, mapping.generatedLine, mapping.generatedCharacter, /*allowEdits*/ true)
                 : -1;
             let source: string | undefined;
             let sourcePosition: number | undefined;
@@ -624,7 +624,7 @@ namespace ts {
                 const sourceFile = host.getSourceFileLike(sourceFileAbsolutePaths[mapping.sourceIndex]);
                 source = map.sources[mapping.sourceIndex];
                 sourcePosition = sourceFile !== undefined
-                    ? getPositionOfLineAndCharacterWithEdits(sourceFile, mapping.sourceLine, mapping.sourceCharacter)
+                    ? getPositionOfLineAndCharacter(sourceFile, mapping.sourceLine, mapping.sourceCharacter, /*allowEdits*/ true)
                     : -1;
             }
             return {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index e654f4faab7..772c42e5aa7 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2615,7 +2615,7 @@ namespace ts {
         readonly text: string;
         lineMap?: ReadonlyArray<number>;
         /* @internal */
-        getPositionOfLineAndCharacter?(line: number, character: number): number;
+        getPositionOfLineAndCharacter?(line: number, character: number, allowEdits?: true): number;
     }
 
 
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 5eb009fcb52..4d3cf160707 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -2316,7 +2316,7 @@ namespace ts.server {
                         const lineOffset = info.positionToLineOffset(pos);
                         return { line: lineOffset.line - 1, character: lineOffset.offset - 1 };
                     },
-                    getPositionOfLineAndCharacter: (line, character) => info.lineOffsetToPosition(line + 1, character + 1)
+                    getPositionOfLineAndCharacter: (line, character, allowEdits) => info.lineOffsetToPosition(line + 1, character + 1, allowEdits)
                 };
             }
             return info.sourceFileLike;
diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index 29685112188..326df8c2219 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -186,9 +186,9 @@ namespace ts.server {
          * @param line 1 based index
          * @param offset 1 based index
          */
-        lineOffsetToPosition(line: number, offset: number): number {
+        lineOffsetToPosition(line: number, offset: number, allowEdits?: true): number {
             if (!this.useScriptVersionCacheIfValidOrOpen()) {
-                return computePositionOfLineAndCharacter(this.getLineMap(), line - 1, offset - 1, this.text);
+                return computePositionOfLineAndCharacter(this.getLineMap(), line - 1, offset - 1, this.text, allowEdits);
             }
 
             // TODO: assert this offset is actually on the line
@@ -586,8 +586,12 @@ namespace ts.server {
          * @param line 1 based index
          * @param offset 1 based index
          */
-        lineOffsetToPosition(line: number, offset: number): number {
-            return this.textStorage.lineOffsetToPosition(line, offset);
+        lineOffsetToPosition(line: number, offset: number): number;
+        /*@internal*/
+        // tslint:disable-next-line:unified-signatures
+        lineOffsetToPosition(line: number, offset: number, allowEdits?: true): number;
+        lineOffsetToPosition(line: number, offset: number, allowEdits?: true): number {
+            return this.textStorage.lineOffsetToPosition(line, offset, allowEdits);
         }
 
         positionToLineOffset(position: number): protocol.Location {
diff --git a/src/services/services.ts b/src/services/services.ts
index e8dfb8640e0..15f9709cb38 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -602,8 +602,8 @@ namespace ts {
             return getLineStarts(this);
         }
 
-        public getPositionOfLineAndCharacter(line: number, character: number): number {
-            return computePositionOfLineAndCharacter(getLineStarts(this), line, character, this.text);
+        public getPositionOfLineAndCharacter(line: number, character: number, allowEdits?: true): number {
+            return computePositionOfLineAndCharacter(getLineStarts(this), line, character, this.text, allowEdits);
         }
 
         public getLineEndOfPosition(pos: number): number {
diff --git a/src/services/sourcemaps.ts b/src/services/sourcemaps.ts
index ce692fc2184..12991d49802 100644
--- a/src/services/sourcemaps.ts
+++ b/src/services/sourcemaps.ts
@@ -97,7 +97,6 @@ namespace ts {
             const fileFromCache = sourceFileLike.get(path);
             if (fileFromCache !== undefined) return fileFromCache ? fileFromCache : undefined;
 
-            // TODO: should ask host instead?
             if (!host.readFile || host.fileExists && !host.fileExists(path)) {
                 sourceFileLike.set(path, false);
                 return undefined;