Index: lib/Driver/ToolChains/Clang.cpp
===================================================================
--- lib/Driver/ToolChains/Clang.cpp
+++ lib/Driver/ToolChains/Clang.cpp
@@ -1856,7 +1856,8 @@
     Buf = ".";
   CDB << "{ \"directory\": \"" << escape(Buf) << "\"";
   CDB << ", \"file\": \"" << escape(Input.getFilename()) << "\"";
-  CDB << ", \"output\": \"" << escape(Output.getFilename()) << "\"";
+  if (!Output.isNothing())
+    CDB << ", \"output\": \"" << escape(Output.getFilename()) << "\"";
   CDB << ", \"arguments\": [\"" << escape(D.ClangExecutable) << "\"";
   Buf = "-x";
   Buf += types::getTypeName(Input.getType());
Index: test/Driver/compilation_database.c
===================================================================
--- test/Driver/compilation_database.c
+++ test/Driver/compilation_database.c
@@ -1,10 +1,12 @@
 // RUN: mkdir -p %t && cd %t
 // RUN: %clang -MD -MP --sysroot=somewhere -c -x c %s -xc++ %s -Wall -MJ - -no-canonical-prefixes 2>&1 | FileCheck %s
 // RUN: not %clang -c -x c %s -MJ %s/non-existant -no-canonical-prefixes 2>&1 | FileCheck --check-prefix=ERROR %s
+// RUN: %clang %s --sysroot=somewhere -MJ - -fsyntax-only -no-canonical-prefixes 2>&1 | FileCheck --check-prefix=FSYNTAX-ONLY %s
 
 // CHECK: { "directory": "{{.*}}",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "output": "compilation_database.o", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc", "[[SRC]]", "--sysroot=somewhere", "-c", "-Wall",{{.*}} "--target={{[^"]+}}"]},
 // CHECK: { "directory": "{{.*}}",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "output": "compilation_database.o", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc++", "[[SRC]]", "--sysroot=somewhere", "-c", "-Wall",{{.*}} "--target={{[^"]+}}"]},
 // ERROR: error: compilation database '{{.*}}/non-existant' could not be opened:
+// FSYNTAX-ONLY: { "directory": "{{.*}}",  "file": "[[SRC:[^"]+[/|\\]compilation_database.c]]", "arguments": ["{{[^"]*}}clang{{[^"]*}}", "-xc", "[[SRC]]", "--sysroot=somewhere", {{.*}} "--target={{[^"]+}}"]},
 
 int main(void) {
   return 0;