diff --git a/lib/MC/MCParser/AsmParser.cpp b/lib/MC/MCParser/AsmParser.cpp
index 03b004ecfac..4f7734153ac 100644
--- a/lib/MC/MCParser/AsmParser.cpp
+++ b/lib/MC/MCParser/AsmParser.cpp
@@ -1937,39 +1937,80 @@ bool AsmParser::parseMacroArguments(const MCAsmMacro *M,
                                     MCAsmMacroArguments &A) {
   const unsigned NParameters = M ? M->Parameters.size() : 0;
 
+  A.resize(NParameters);
+  for (unsigned PI = 0; PI < NParameters; ++PI)
+    if (!M->Parameters[PI].second.empty())
+      A[PI] = M->Parameters[PI].second;
+
+  bool NamedParametersFound = false;
+
   // Parse two kinds of macro invocations:
   // - macros defined without any parameters accept an arbitrary number of them
   // - macros defined with parameters accept at most that many of them
   for (unsigned Parameter = 0; !NParameters || Parameter < NParameters;
        ++Parameter) {
-    MCAsmMacroArgument MA;
+    MCAsmMacroParameter FA;
+    SMLoc L;
 
-    if (parseMacroArgument(MA))
+    if (Lexer.is(AsmToken::Identifier) && Lexer.peekTok().is(AsmToken::Equal)) {
+      L = Lexer.getLoc();
+      if (parseIdentifier(FA.first)) {
+        Error(L, "invalid argument identifier for formal argument");
+        eatToEndOfStatement();
+        return true;
+      }
+
+      if (!Lexer.is(AsmToken::Equal)) {
+        TokError("expected '=' after formal parameter identifier");
+        eatToEndOfStatement();
+        return true;
+      }
+      Lex();
+
+      NamedParametersFound = true;
+    }
+
+    if (NamedParametersFound && FA.first.empty()) {
+      Error(Lexer.getLoc(), "cannot mix positional and keyword arguments");
+      eatToEndOfStatement();
+      return true;
+    }
+
+    if (parseMacroArgument(FA.second))
       return true;
 
-    if (!MA.empty() || (!NParameters && !Lexer.is(AsmToken::EndOfStatement)))
-      A.push_back(MA);
-    else if (NParameters) {
-      if (!M->Parameters[Parameter].second.empty())
-        A.push_back(M->Parameters[Parameter].second);
-      else
-        A.push_back(MA);
+    unsigned PI = Parameter;
+    if (!FA.first.empty()) {
+      unsigned FAI = 0;
+      for (FAI = 0; FAI < NParameters; ++FAI)
+        if (M->Parameters[FAI].first == FA.first)
+          break;
+      if (FAI >= NParameters) {
+        Error(L,
+              "parameter named '" + FA.first + "' does not exist for macro '" +
+              M->Name + "'");
+        return true;
+      }
+      PI = FAI;
+    }
+
+    if (!FA.second.empty()) {
+      if (A.size() <= PI)
+        A.resize(PI + 1);
+      A[PI] = FA.second;
     }
 
     // At the end of the statement, fill in remaining arguments that have
     // default values. If there aren't any, then the next argument is
     // required but missing
-    if (Lexer.is(AsmToken::EndOfStatement)) {
-      if (NParameters && Parameter < NParameters - 1) {
-        continue;
-      }
+    if (Lexer.is(AsmToken::EndOfStatement))
       return false;
-    }
 
     if (Lexer.is(AsmToken::Comma))
       Lex();
   }
-  return TokError("Too many arguments");
+
+  return TokError("too many positional arguments");
 }
 
 const MCAsmMacro *AsmParser::lookupMacro(StringRef Name) {
diff --git a/test/MC/AsmParser/macro-err1.s b/test/MC/AsmParser/macro-err1.s
index 924deb0cf6e..bd9c837d8be 100644
--- a/test/MC/AsmParser/macro-err1.s
+++ b/test/MC/AsmParser/macro-err1.s
@@ -7,4 +7,4 @@
 
 foo 42,  42
 
-// CHECK: Too many arguments
+// CHECK: too many positional arguments
diff --git a/test/MC/AsmParser/macros-argument-parsing-diagnostics.s b/test/MC/AsmParser/macros-argument-parsing-diagnostics.s
new file mode 100644
index 00000000000..a1970e0c9d5
--- /dev/null
+++ b/test/MC/AsmParser/macros-argument-parsing-diagnostics.s
@@ -0,0 +1,24 @@
+# RUN: not llvm-mc -triple i386 -filetype asm -o /dev/null %s 2>&1 | FileCheck %s
+
+	.macro double first = -1, second = -1
+		# begin entry
+		.long \first
+		.long \second
+		# end entry
+	.endm
+
+	double 0, 1, 2
+# CHECK: error: too many positional arguments
+# CHECK: 	double 0, 1, 2
+# CHECK:                     ^
+
+	double second = 1, 2
+# CHECK: error: cannot mix positional and keyword arguments
+# CHECK: 	double second = 1, 2
+# CHECK:                           ^
+
+	double third = 0
+# CHECK: error: parameter named 'third' does not exist for macro 'double'
+# CHECK: 	double third = 0
+# CHECK:               ^
+
diff --git a/test/MC/AsmParser/macros-argument-parsing.s b/test/MC/AsmParser/macros-argument-parsing.s
index 097a2702a06..11da298e00e 100644
--- a/test/MC/AsmParser/macros-argument-parsing.s
+++ b/test/MC/AsmParser/macros-argument-parsing.s
@@ -8,3 +8,54 @@
 
 # CHECK: .long 1
 
+	.macro double first = -1, second = -1
+		# begin entry
+		.long \first
+		.long \second
+		# end entry
+	.endm
+
+	double
+# CHECK: .long -1
+# CHECK: .long -1
+
+	double 1
+# CHECK: .long 1
+# CHECK: .long -1
+
+	double 2, 3
+# CHECK: .long 2
+# CHECK: .long 3
+
+	double , 4
+# CHECK: .long -1
+# CHECK: .long 4
+
+	double 5, second = 6
+# CHECK: .long 5
+# CHECK: .long 6
+
+	double first = 7
+# CHECK: .long 7
+# CHECK: .long -1
+
+	double second = 8
+# CHECK: .long -1
+# CHECK: .long 8
+
+	double second = 9, first = 10
+# CHECK: .long 10
+# CHECK: .long 9
+
+	double second + 11
+# CHECK: .long second+11
+# CHECK: .long -1
+
+	double , second + 12
+# CHECK: .long -1
+# CHECK: .long second+12
+
+	double second
+# CHECK: .long second
+# CHECK: .long -1
+