diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -943,9 +943,8 @@
       getSourceManager().clearIDTables();
 
     if (Act.BeginSourceFile(*this, FIF)) {
-      if (llvm::Error Err = Act.Execute()) {
-        consumeError(std::move(Err)); // FIXME this drops errors on the floor.
-      }
+      if (llvm::Error Err = Act.Execute())
+        OS << "Internal compiler error: " << toString(std::move(Err)) << "\n";
       Act.EndSourceFile();
     }
   }
diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -940,15 +940,10 @@
       CI.hasPreprocessor()) {
     StringRef Cache =
         CI.getPreprocessor().getHeaderSearchInfo().getModuleCachePath();
-    if (!Cache.empty()) {
+    if (!Cache.empty())
       if (llvm::Error Err = GlobalModuleIndex::writeIndex(
-              CI.getFileManager(), CI.getPCHContainerReader(), Cache)) {
-        // FIXME this drops the error on the floor, but
-        // Index/pch-from-libclang.c seems to rely on dropping at least some of
-        // the error conditions!
-        consumeError(std::move(Err));
-      }
-    }
+              CI.getFileManager(), CI.getPCHContainerReader(), Cache))
+        return Err;
   }
 
   return llvm::Error::success();
diff --git a/clang/lib/Serialization/GlobalModuleIndex.cpp b/clang/lib/Serialization/GlobalModuleIndex.cpp
--- a/clang/lib/Serialization/GlobalModuleIndex.cpp
+++ b/clang/lib/Serialization/GlobalModuleIndex.cpp
@@ -860,7 +860,9 @@
   llvm::LockFileManager Locked(IndexPath);
   switch (Locked) {
   case llvm::LockFileManager::LFS_Error:
-    return llvm::createStringError(std::errc::io_error, "LFS error");
+    return llvm::createStringError(
+        std::errc::io_error, "LFS error for \"%s\": %s", IndexPath.c_str(),
+        Locked.getErrorMessage().c_str());
 
   case llvm::LockFileManager::LFS_Owned:
     // We're responsible for building the index ourselves. Do so below.
@@ -869,8 +871,10 @@
   case llvm::LockFileManager::LFS_Shared:
     // Someone else is responsible for building the index. We don't care
     // when they finish, so we're done.
-    return llvm::createStringError(std::errc::device_or_resource_busy,
-                                   "someone else is building the index");
+    return llvm::createStringError(
+        std::errc::device_or_resource_busy,
+        "someone else is building the index \"%s\": %s", IndexPath.c_str(),
+        Locked.getErrorMessage().c_str());
   }
 
   // The module index builder.