diff --git a/clang/lib/Lex/TokenLexer.cpp b/clang/lib/Lex/TokenLexer.cpp
index f1af42aea5172512d4e9677bdb2e497ae06c64bb..65d083dffdca0cfc727028dadd0c646d2ac0832f 100644
--- a/clang/lib/Lex/TokenLexer.cpp
+++ b/clang/lib/Lex/TokenLexer.cpp
@@ -223,7 +223,11 @@ void TokenLexer::ExpandFunctionArguments() {
       // If the next token was supposed to get leading whitespace, ensure it has
       // it now.
       if (CurTok.hasLeadingSpace() || NextTokGetsSpace) {
-        ResultToks[ResultToks.size()-NumToks].setFlag(Token::LeadingSpace);
+        // Exception: the RHS of a paste doesn't get whitespace. This allows
+        // constructs like conacatenating a period and an identifer to work
+        // correctly in assembler-with-cpp.
+        if (!PasteBefore)
+          ResultToks[ResultToks.size()-NumToks].setFlag(Token::LeadingSpace);
         NextTokGetsSpace = false;
       }
       continue;
diff --git a/clang/test/Preprocessor/assembler-with-cpp.c b/clang/test/Preprocessor/assembler-with-cpp.c
index 885e67b98c8fdd172cf2c216ec76f62b300a2669..bb1688057855dcc74606e02f533b9945c38765ba 100644
--- a/clang/test/Preprocessor/assembler-with-cpp.c
+++ b/clang/test/Preprocessor/assembler-with-cpp.c
@@ -63,4 +63,9 @@ T7(foo)
 // RUN: grep 'T6 #nostring' %t &&
 // RUN: grep 'T7 "foo"' %t &&
 
+// Concatenation with period doesn't leave a space
+// RUN: grep '.T8' %t &&
+#define T8(A,B) A ## B
+T8(.,T8)
+
 // RUN: true