Index: test/FileCheck/defines.txt
===================================================================
--- test/FileCheck/defines.txt
+++ test/FileCheck/defines.txt
@@ -3,16 +3,19 @@
 ;
 ; RUN: not FileCheck -DVALUE=10 -check-prefix NOT -input-file %s %s 2>&1 | FileCheck %s -check-prefix NOT-ERRMSG
 ; RUN: FileCheck -DVALUE=20 -check-prefix NOT -input-file %s %s
+; RUN: not FileCheck -DVALUE10 -input-file %s %s 2>&1 | FileCheck %s -check-prefix ERRCLI
 
 Value = 10
 ; CHECK: Value = [[VALUE]]
 ; NOT-NOT: Value = [[VALUE]]
 
-; ERRMSG: defines.txt:8:10: error: CHECK: expected string not found in input
+; ERRMSG: defines.txt:9:10: error: CHECK: expected string not found in input
 ; ERRMSG: defines.txt:1:1: note: scanning from here
 ; ERRMSG: defines.txt:1:1: note: with variable "VALUE" equal to "20"
-; ERRMSG: defines.txt:7:1: note: possible intended match here
+; ERRMSG: defines.txt:8:1: note: possible intended match here
 
-; NOT-ERRMSG: defines.txt:9:12: error: {{NOT}}-NOT: excluded string found in input
-; NOT-ERRMSG: defines.txt:7:1: note: found here
-; NOT-ERRMSG: defines.txt:7:1: note: with variable "VALUE" equal to "10"
\ No newline at end of file
+; NOT-ERRMSG: defines.txt:10:12: error: {{NOT}}-NOT: excluded string found in input
+; NOT-ERRMSG: defines.txt:8:1: note: found here
+; NOT-ERRMSG: defines.txt:8:1: note: with variable "VALUE" equal to "10"
+
+; ERRCLI: Command-line definition 'VALUE10' missing equal sign
Index: utils/FileCheck/FileCheck.cpp
===================================================================
--- utils/FileCheck/FileCheck.cpp
+++ utils/FileCheck/FileCheck.cpp
@@ -523,8 +523,17 @@
   for (auto CheckNot : ImplicitCheckNot)
     Req.ImplicitCheckNot.push_back(CheckNot);
 
-  for (auto G : GlobalDefines)
+  bool GlobalDefineError = false;
+  for (auto G : GlobalDefines) {
+    if (G.find('=') == std::string::npos) {
+      errs() << "Command-line definition '" << G << "' missing equal sign\n";
+      GlobalDefineError = true;
+      continue;
+    }
     Req.GlobalDefines.push_back(G);
+  }
+  if (GlobalDefineError)
+    return 2;
 
   Req.AllowEmptyInput = AllowEmptyInput;
   Req.EnableVarScope = EnableVarScope;