diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 880221176027e9..062fbd2e4c0a44 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -8124,7 +8124,7 @@ def show_inst : Flag<["-"], "show-inst">,
 def dwarf_debug_producer : Separate<["-"], "dwarf-debug-producer">,
   HelpText<"The string to embed in the Dwarf debug AT_producer record.">;
 
-def defsym : Separate<["-"], "defsym">,
+def defsym : Separate<["--"], "defsym">,
   HelpText<"Define a value for a symbol">;
 
 } // let Visibility = [CC1AsOption]
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index acd32bddea6b65..331cf6e713d890 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2666,7 +2666,7 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
           D.Diag(diag::err_drv_defsym_invalid_symval) << SVal;
           break;
         }
-        CmdArgs.push_back(Value.data());
+        CmdArgs.push_back("--defsym");
         TakeNextArg = true;
       } else if (Value == "-fdebug-compilation-dir") {
         CmdArgs.push_back("-fdebug-compilation-dir");
diff --git a/clang/test/Driver/defsym.s b/clang/test/Driver/defsym.s
index d152b326ae8b18..af66656cce15e1 100644
--- a/clang/test/Driver/defsym.s
+++ b/clang/test/Driver/defsym.s
@@ -6,9 +6,10 @@
 
 // RUN: %clang -### -c -no-integrated-as -target x86_64-unknown-unknown %s \
 // RUN: -Wa,-defsym,abc=5 -Wa,--defsym,xyz=0xa \
-// RUN: 2>&1 | FileCheck %s --check-prefix=CHECK-DEFSYM1
+// RUN: 2>&1 | FileCheck %s --check-prefix=CHECK-DEFSYM1-GAS
 
-// CHECK-DEFSYM1: "-defsym" "abc=5" "--defsym" "xyz=0xa"
+// CHECK-DEFSYM1: "--defsym" "abc=5" "--defsym" "xyz=0xa"
+// CHECK-DEFSYM1-GAS: "-defsym" "abc=5" "--defsym" "xyz=0xa"
 
 // RUN: not %clang -c -integrated-as -o /dev/null %s \
 // RUN: -Wa,-defsym,abc= \
diff --git a/clang/test/Misc/cc1as-defsym.s b/clang/test/Misc/cc1as-defsym.s
new file mode 100644
index 00000000000000..0dc7f24dac2c0b
--- /dev/null
+++ b/clang/test/Misc/cc1as-defsym.s
@@ -0,0 +1,12 @@
+// REQUIRES: x86-registered-target
+// RUN: %clang -cc1as -triple x86_64 -filetype obj --defsym A=1 %s -o %t.o
+// RUN: llvm-nm %t.o | FileCheck %s
+
+// CHECK: 0000000000000001 A foo
+
+.globl foo
+.ifdef A
+foo = 1
+.else
+foo = 0
+.endif