Index: llvm/test/tools/llvm-rc/flags.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-rc/flags.test
@@ -0,0 +1,4 @@
+; RUN: llvm-rc /dry-run /FO %t %p/Inputs/empty.rc 2>&1 | FileCheck %s --allow-empty --check-prefix=FO
+; RUN: llvm-rc /dry-run /FO%t %p/Inputs/empty.rc 2>&1 | FileCheck %s --allow-empty --check-prefix=FO
+
+; FO-NOT: Exactly one input file should be provided.
Index: llvm/tools/llvm-rc/Opts.td
===================================================================
--- llvm/tools/llvm-rc/Opts.td
+++ llvm/tools/llvm-rc/Opts.td
@@ -4,7 +4,7 @@
 // These options seem to be important for the tool
 // and should be implemented.
 
-def FILEOUT : Separate<[ "/", "-" ], "FO">,
+def FILEOUT : JoinedOrSeparate<[ "/", "-" ], "FO">,
               HelpText<"Change the output file location.">;
 
 def DEFINE : Separate<[ "/", "-" ], "D">,