diff --git a/Jakefile.js b/Jakefile.js
index 633e4f45cb6..7a16c681b6e 100644
--- a/Jakefile.js
+++ b/Jakefile.js
@@ -204,7 +204,7 @@ task(TaskNames.lint, [TaskNames.buildRules], () => {
         if (fold.isTravis()) console.log(fold.end("lint"));
         complete();
     }));
-});
+}, { async: true });
 
 desc("Diffs the compiler baselines using the diff tool specified by the 'DIFF' environment variable");
 task('diff', function () {
diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index 80f6d1c1cc8..97b7c0afad7 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -777,6 +777,7 @@ namespace ts {
 
             let pseudoUpToDate = false;
             let usesPrepend = false;
+            let upstreamChangedProject: string | undefined;
             if (project.projectReferences) {
                 for (const ref of project.projectReferences) {
                     usesPrepend = usesPrepend || !!(ref.prepend);
@@ -809,6 +810,7 @@ namespace ts {
                     // *after* those files, then we're "psuedo up to date" and eligible for a fast rebuild
                     if (refStatus.newestDeclarationFileContentChangedTime <= oldestOutputFileTime) {
                         pseudoUpToDate = true;
+                        upstreamChangedProject = ref.path;
                         continue;
                     }
 
@@ -837,8 +839,12 @@ namespace ts {
                 };
             }
 
-            if (usesPrepend) {
-                pseudoUpToDate = false;
+            if (usesPrepend && pseudoUpToDate) {
+                return {
+                    type: UpToDateStatusType.OutOfDateWithUpstream,
+                    outOfDateOutputFileName: oldestOutputFileName,
+                    newerProjectName: upstreamChangedProject!
+                };
             }
 
             // Up to date
diff --git a/src/testRunner/unittests/tsbuild.ts b/src/testRunner/unittests/tsbuild.ts
index 2ae034ff673..bd40c7297d9 100644
--- a/src/testRunner/unittests/tsbuild.ts
+++ b/src/testRunner/unittests/tsbuild.ts
@@ -259,6 +259,23 @@ namespace ts {
                 });
             });
         });
+
+        describe("tsbuild - downstream prepend projects always get rebuilt", () => {
+            const fs = outFileFs.shadow();
+            const host = new fakes.CompilerHost(fs);
+            const builder = createSolutionBuilder(host, buildHost, ["/src/third"], { dry: false, force: false, verbose: false });
+            clearDiagnostics();
+            builder.buildAllProjects();
+            assertDiagnosticMessages(/*none*/);
+            assert.equal(fs.statSync("src/third/thirdjs/output/third-output.js").mtimeMs, time(), "First build timestamp is correct");
+            tick();
+            replaceText(fs, "src/first/first_PART1.ts", "Hello", "Hola");
+            tick();
+            builder.resetBuildContext();
+            builder.buildAllProjects();
+            assertDiagnosticMessages(/*none*/);
+            assert.equal(fs.statSync("src/third/thirdjs/output/third-output.js").mtimeMs, time(), "Second build timestamp is correct");
+        });
     }
 
     describe("tsbuild - graph-ordering", () => {
diff --git a/tests/projects/outfile-concat/first/tsconfig.json b/tests/projects/outfile-concat/first/tsconfig.json
index 8370f6512b8..f71a8182585 100644
--- a/tests/projects/outfile-concat/first/tsconfig.json
+++ b/tests/projects/outfile-concat/first/tsconfig.json
@@ -9,6 +9,11 @@
     "declaration": true,
     "outFile": "./bin/first-output.js"
   },
+  "files": [
+    "first_PART1.ts",
+    "first_part2.ts",
+    "first_part3.ts"
+  ],
   "references": [
   ]
 }
diff --git a/tests/projects/outfile-concat/third/tsconfig.json b/tests/projects/outfile-concat/third/tsconfig.json
index 18c98608db1..fef85ce8927 100644
--- a/tests/projects/outfile-concat/third/tsconfig.json
+++ b/tests/projects/outfile-concat/third/tsconfig.json
@@ -9,6 +9,9 @@
     "declaration": true,
     "outFile": "./thirdjs/output/third-output.js"
   },
+  "files": [
+    "third_part1.ts"
+  ],
   "references": [
     { "path": "../first", "prepend": true },
     { "path": "../second", "prepend": true },