Index: lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
===================================================================
--- lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -2282,9 +2282,9 @@
   const AsmToken &Tok = Parser.getTok();
   if (Tok.is(AsmToken::Real) || Tok.is(AsmToken::Integer)) {
     int64_t Val;
-    if (Tok.is(AsmToken::Integer) && !isNegative && Tok.getString().startswith("0x")) {
+    if (Tok.is(AsmToken::Integer) && Tok.getString().startswith("0x")) {
       Val = Tok.getIntVal();
-      if (Val > 255 || Val < 0) {
+      if (Val > 255 || isNegative) {
         TokError("encoded floating point value out of range");
         return MatchOperand_ParseFail;
       }
Index: test/MC/AArch64/neon-diagnostics.s
===================================================================
--- test/MC/AArch64/neon-diagnostics.s
+++ test/MC/AArch64/neon-diagnostics.s
@@ -279,10 +279,15 @@
 //----------------------------------------------------------------------
         // invalid vector type (2s, 4s, 2d)
          fmov v0.4h, #1.0
+         // invalid immediate (negative hexadecimal encoding)
+         fmov v0.4s, #-0x0
 
 // CHECK:ERROR: error: invalid operand for instruction
 // CHECK:ERROR:         fmov v0.4h, #1.0
 // CHECK:ERROR:              ^
+// CHECK-ERROR: error: encoded floating point value out of range
+// CHECK-ERROR:         fmov v0.4s, #-0x0
+// CHECK-ERROR:                     ^
 
 //----------------------------------------------------------------------
 // Vector Move -  register