diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 80115dbd35dab..7017f138224e9 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2829,14 +2829,14 @@ namespace ts {
                     redirectTargetsMap.add(fileFromPackageId.path, fileName);
                     addFileToFilesByName(dupFile, path, redirectedPath);
                     addFileIncludeReason(dupFile, reason);
-                    sourceFileToPackageName.set(path, packageId.name);
+                    sourceFileToPackageName.set(path, packageIdToPackageName(packageId));
                     processingOtherFiles!.push(dupFile);
                     return dupFile;
                 }
                 else if (file) {
                     // This is the first source file to have this packageId.
                     packageIdToSourceFile.set(packageIdKey, file);
-                    sourceFileToPackageName.set(path, packageId.name);
+                    sourceFileToPackageName.set(path, packageIdToPackageName(packageId));
                 }
             }
             addFileToFilesByName(file, path, redirectedPath);
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 691a965ee661d..ed8ddf17227a0 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -192,9 +192,12 @@ namespace ts {
         return a === b || !!a && !!b && a.name === b.name && a.subModuleName === b.subModuleName && a.version === b.version;
     }
 
-    export function packageIdToString({ name, subModuleName, version }: PackageId): string {
-        const fullName = subModuleName ? `${name}/${subModuleName}` : name;
-        return `${fullName}@${version}`;
+    export function packageIdToPackageName({ name, subModuleName }: PackageId): string {
+        return subModuleName ? `${name}/${subModuleName}` : name;
+    }
+
+    export function packageIdToString(packageId: PackageId): string {
+        return `${packageIdToPackageName(packageId)}@${packageId.version}`;
     }
 
     export function typeDirectiveIsEqualTo(oldResolution: ResolvedTypeReferenceDirective, newResolution: ResolvedTypeReferenceDirective): boolean {
diff --git a/src/testRunner/unittests/reuseProgramStructure.ts b/src/testRunner/unittests/reuseProgramStructure.ts
index 6dc13de241d47..3e9e5f2313441 100644
--- a/src/testRunner/unittests/reuseProgramStructure.ts
+++ b/src/testRunner/unittests/reuseProgramStructure.ts
@@ -234,7 +234,7 @@ namespace ts {
             });
             assert.equal(program2.structureIsReused, StructureIsReused.Completely);
             const program1Diagnostics = program1.getSemanticDiagnostics(program1.getSourceFile("a.ts"));
-            const program2Diagnostics = program2.getSemanticDiagnostics(program1.getSourceFile("a.ts"));
+            const program2Diagnostics = program2.getSemanticDiagnostics(program2.getSourceFile("a.ts"));
             assert.equal(program1Diagnostics.length, program2Diagnostics.length);
         });
 
@@ -245,7 +245,26 @@ namespace ts {
             });
             assert.equal(program2.structureIsReused, StructureIsReused.Completely);
             const program1Diagnostics = program1.getSemanticDiagnostics(program1.getSourceFile("a.ts"));
-            const program2Diagnostics = program2.getSemanticDiagnostics(program1.getSourceFile("a.ts"));
+            const program2Diagnostics = program2.getSemanticDiagnostics(program2.getSourceFile("a.ts"));
+            assert.equal(program1Diagnostics.length, program2Diagnostics.length);
+        });
+
+        it("successful if change affects a single module of a package", () => {
+            const files = [
+                { name: "/a.ts", text: SourceText.New("", "import {b} from 'b'", "var a = b;") },
+                { name: "/node_modules/b/index.d.ts", text: SourceText.New("", "export * from './internal';", "") },
+                { name: "/node_modules/b/internal.d.ts", text: SourceText.New("", "", "export const b = 1;") },
+                { name: "/node_modules/b/package.json", text: SourceText.New("", "", JSON.stringify({ name: "b", version: "1.2.3" })) },
+            ];
+
+            const options: CompilerOptions = { target, moduleResolution: ModuleResolutionKind.NodeJs };
+            const program1 = newProgram(files, ["/a.ts"], options);
+            const program2 = updateProgram(program1, ["/a.ts"], options, files => {
+                files[2].text = files[2].text.updateProgram("export const b = 2;");
+            });
+            assert.equal(program2.structureIsReused, StructureIsReused.Completely);
+            const program1Diagnostics = program1.getSemanticDiagnostics(program1.getSourceFile("a.ts"));
+            const program2Diagnostics = program2.getSemanticDiagnostics(program2.getSourceFile("a.ts"));
             assert.equal(program1Diagnostics.length, program2Diagnostics.length);
         });