Index: lib/Target/Mips/Mips32r6InstrInfo.td
===================================================================
--- lib/Target/Mips/Mips32r6InstrInfo.td
+++ lib/Target/Mips/Mips32r6InstrInfo.td
@@ -34,7 +34,6 @@
 // Removed: ldxc1
 // Removed: luxc1
 // Removed: lwxc1
-// Removed: prefx
 // Removed: sdxc1
 // Removed: suxc1
 // Removed: swxc1
Index: test/MC/Mips/mips32r6/invalid-mips4-wrong-error.s
===================================================================
--- /dev/null
+++ test/MC/Mips/mips32r6/invalid-mips4-wrong-error.s
@@ -0,0 +1,21 @@
+# Instructions that are invalid and are correctly rejected but use the wrong
+# error message at the moment.
+#
+# RUN: not llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r6 \
+# RUN:     2>%t1
+# RUN: FileCheck %s < %t1
+
+        .set noat
+        beql $1,$2,4            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgezall $3,8            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgezl $3,8              # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgtzl $4,16             # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        blezl $3,8              # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bltzall $3,8            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bltzl $4,16             # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bnel $1,$2,4            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc1tl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc1fl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc2tl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc2fl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        prefx 0,$2($31)         # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
Index: test/MC/Mips/mips64r6/invalid-mips4-wrong-error.s
===================================================================
--- /dev/null
+++ test/MC/Mips/mips64r6/invalid-mips4-wrong-error.s
@@ -0,0 +1,21 @@
+# Instructions that are invalid and are correctly rejected but use the wrong
+# error message at the moment.
+#
+# RUN: not llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r6 \
+# RUN:     2>%t1
+# RUN: FileCheck %s < %t1
+
+        .set noat
+        beql $1,$2,4            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgezall $3,8            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgezl $3,8              # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bgtzl $4,16             # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        blezl $3,8              # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bltzall $3,8            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bltzl $4,16             # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bnel $1,$2,4            # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc1tl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc1fl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc2tl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        bc2fl 4                 # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction
+        prefx 0,$2($31)         # CHECK: :[[@LINE]]:{{[0-9]+}}: error: Unknown instruction