Index: lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
===================================================================
--- lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -1271,9 +1271,11 @@
   bool isExtend64() const {
     if (!isExtend())
       return false;
-    // UXTX and SXTX require a 64-bit source register (the ExtendLSL64 class).
+    // Make sure the extend expects a 32-bit source register.
     AArch64_AM::ShiftExtendType ET = getShiftExtendType();
-    return ET != AArch64_AM::UXTX && ET != AArch64_AM::SXTX;
+    return ET == AArch64_AM::UXTB || ET == AArch64_AM::SXTB ||
+           ET == AArch64_AM::UXTH || ET == AArch64_AM::SXTH ||
+           ET == AArch64_AM::UXTW || ET == AArch64_AM::SXTW;
   }
 
   bool isExtendLSL64() const {
@@ -4199,7 +4201,7 @@
     return Error(Loc, "expected AArch64 condition code");
   case Match_AddSubRegExtendSmall:
     return Error(Loc,
-      "expected '[su]xt[bhw]' or 'lsl' with optional integer in range [0, 4]");
+      "expected '[su]xt[bhw]' with optional integer in range [0, 4]");
   case Match_AddSubRegExtendLarge:
     return Error(Loc,
       "expected 'sxtx' 'uxtx' or 'lsl' with optional integer in range [0, 4]");
Index: test/MC/AArch64/basic-a64-diagnostics.s
===================================================================
--- test/MC/AArch64/basic-a64-diagnostics.s
+++ test/MC/AArch64/basic-a64-diagnostics.s
@@ -8,13 +8,17 @@
         // Mismatched final register and extend
         add x2, x3, x5, sxtb
         add x2, x4, w2, uxtx
+        add x2, x4, w2, lsl #3
         add w5, w7, x9, sxtx
 // CHECK-ERROR: error: expected 'sxtx' 'uxtx' or 'lsl' with optional integer in range [0, 4]
 // CHECK-ERROR:         add x2, x3, x5, sxtb
 // CHECK-ERROR:                         ^
-// CHECK-ERROR: error: expected '[su]xt[bhw]' or 'lsl' with optional integer in range [0, 4]
+// CHECK-ERROR: error: expected '[su]xt[bhw]' with optional integer in range [0, 4]
 // CHECK-ERROR:         add x2, x4, w2, uxtx
 // CHECK-ERROR:                         ^
+// CHECK-ERROR: error: expected '[su]xt[bhw]' with optional integer in range [0, 4]
+// CHECK-ERROR:         add x2, x4, w2, lsl #3
+// CHECK-ERROR:                         ^
 // CHECK-ERROR: error: expected compatible register, symbol or integer in range [0, 4095]
 // CHECK-ERROR:         add w5, w7, x9, sxtx
 // CHECK-ERROR:                     ^
@@ -26,7 +30,7 @@
 // CHECK-ERROR: error: expected integer shift amount
 // CHECK-ERROR:         add x9, x10, w11, uxtb #-1
 // CHECK-ERROR:                                 ^
-// CHECK-ERROR: error: expected '[su]xt[bhw]' or 'lsl' with optional integer in range [0, 4]
+// CHECK-ERROR: error: expected '[su]xt[bhw]' with optional integer in range [0, 4]
 // CHECK-ERROR:         add x3, x5, w7, uxtb #5
 // CHECK-ERROR:                         ^
 // CHECK-ERROR: error: expected 'sxtx' 'uxtx' or 'lsl' with optional integer in range [0, 4]