diff --git a/llvm/include/llvm/MC/MCContext.h b/llvm/include/llvm/MC/MCContext.h
--- a/llvm/include/llvm/MC/MCContext.h
+++ b/llvm/include/llvm/MC/MCContext.h
@@ -687,15 +687,15 @@
                                                   const Twine &Msg);
 
     const MCAsmMacro *lookupMacro(StringRef Name) {
-      StringMap<MCAsmMacro>::iterator I = MacroMap.find(Name);
+      StringMap<MCAsmMacro>::iterator I = MacroMap.find(Name.lower());
       return (I == MacroMap.end()) ? nullptr : &I->getValue();
     }
 
     void defineMacro(StringRef Name, MCAsmMacro Macro) {
-      MacroMap.insert(std::make_pair(Name, std::move(Macro)));
+      MacroMap.insert(std::make_pair(Name.lower(), std::move(Macro)));
     }
 
-    void undefineMacro(StringRef Name) { MacroMap.erase(Name); }
+    void undefineMacro(StringRef Name) { MacroMap.erase(Name.lower()); }
   };
 
 } // end namespace llvm
diff --git a/llvm/test/MC/X86/macro_case.s b/llvm/test/MC/X86/macro_case.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/X86/macro_case.s
@@ -0,0 +1,10 @@
+# RUN: llvm-mc -filetype=obj -triple=i386 %s -o /dev/null
+
+.macro  mySum from=0, to=5
+        .long   \from
+        .if     \to-\from
+        mySum     "(\from+1)",\to
+        .endif
+        .endm
+
+Mysum 0,5