diff --git a/src/compiler/resolutionCache.ts b/src/compiler/resolutionCache.ts
index ff09efb05ea..6e0384219a1 100644
--- a/src/compiler/resolutionCache.ts
+++ b/src/compiler/resolutionCache.ts
@@ -716,7 +716,7 @@ namespace ts {
                     }
                     // prevent saving an open file from over-eagerly triggering invalidation
                     if (resolutionHost.fileIsOpen(fileOrDirectoryPath)) {
-                        return;
+                        return false;
                     }
                     // Ignore emits from the program
                     if (isEmittedFileOfProgram(resolutionHost.getCurrentProgram(), fileOrDirectoryPath)) {
diff --git a/src/compiler/watch.ts b/src/compiler/watch.ts
index 0faf9f0c175..dbc78fa5d4e 100644
--- a/src/compiler/watch.ts
+++ b/src/compiler/watch.ts
@@ -691,7 +691,7 @@ namespace ts {
             hasChangedAutomaticTypeDirectiveNames = true;
             scheduleProgramUpdate();
         };
-        compilerHost.fileIsOpen = () => false;
+        compilerHost.fileIsOpen = returnFalse;
         compilerHost.maxNumberOfFilesToIterateForInvalidation = host.maxNumberOfFilesToIterateForInvalidation;
         compilerHost.getCurrentProgram = getCurrentProgram;
         compilerHost.writeLog = writeLog;