diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index 3e1811a092d..8f3a1b6f686 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -11780,8 +11780,8 @@ output_insn (const struct last_insn *last_insn)
 	{
 	  j = encoding_length (insn_start_frag, insn_start_off, frag_more (0));
 	  if (j > 15)
-	    as_warn (_("instruction length of %u bytes exceeds the limit of 15"),
-		     j);
+	    as_bad (_("instruction length of %u bytes exceeds the limit of 15"),
+		    j);
 	  else if (fragP)
 	    {
 	      /* NB: Don't add prefix with GOTPC relocation since
diff --git a/gas/testsuite/gas/i386/oversized16.l b/gas/testsuite/gas/i386/oversized16.l
index 3bf7e1d8095..e0fc7619bdc 100644
--- a/gas/testsuite/gas/i386/oversized16.l
+++ b/gas/testsuite/gas/i386/oversized16.l
@@ -1,9 +1,9 @@
 .*: Assembler messages:
-.*:6: Warning: instruction length.*
-.*:7: Warning: instruction length.*
-.*:8: Warning: instruction length.*
-.*:10: Warning: instruction length.*
-.*:11: Warning: instruction length.*
+.*:6: Error: instruction length.*
+.*:7: Error: instruction length.*
+.*:8: Error: instruction length.*
+.*:10: Error: instruction length.*
+.*:11: Error: instruction length.*
 GAS LISTING .*
 
 
@@ -12,29 +12,29 @@ GAS LISTING .*
 [ 	]*3[ 	]+\.code16
 [ 	]*4[ 	]+
 [ 	]*5[ 	]+long16:
-[ 	]*6[ 	]+0000 26678FEA[ 	]+lwpins	eax, es:\[eax\*8\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*6[ 	]+\?\?\?\? 26678FEA[ 	]+lwpins	eax, es:\[eax\*8\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*6[ 	]+781204C5[ 	]*
 [ 	]*6[ 	]+00000000[ 	]*
 [ 	]*6[ 	]+44332211[ 	]*
-[ 	]*7[ 	]+0010 26678FEA[ 	]+lwpval	eax, es:\[eax\*4\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*7[ 	]+\?\?\?\? 26678FEA[ 	]+lwpval	eax, es:\[eax\*4\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*7[ 	]+78120C85[ 	]*
 [ 	]*7[ 	]+00000000[ 	]*
 [ 	]*7[ 	]+44332211[ 	]*
-[ 	]*8[ 	]+0020 26678FEA[ 	]+bextr	eax, es:\[eax\*2\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*8[ 	]+\?\?\?\? 26678FEA[ 	]+bextr	eax, es:\[eax\*2\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*8[ 	]+78100445[ 	]*
 [ 	]*8[ 	]+00000000[ 	]*
 [ 	]*8[ 	]+44332211[ 	]*
 [ 	]*9[ 	]+
-[ 	]*10[ 	]+0030 266766F2[ 	]+xacquire lock add dword ptr es:\[eax\*2\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*10[ 	]+\?\?\?\? 266766F2[ 	]+xacquire lock add dword ptr es:\[eax\*2\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*10[ 	]+F0810445[ 	]*
 [ 	]*10[ 	]+00000000[ 	]*
 [ 	]*10[ 	]+44332211[ 	]*
-[ 	]*11[ 	]+0040 266766F3[ 	]+xrelease lock sub dword ptr es:\[eax\*2\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*11[ 	]+\?\?\?\? 266766F3[ 	]+xrelease lock sub dword ptr es:\[eax\*2\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*11[ 	]+F0812C45[ 	]*
 [ 	]*11[ 	]+00000000[ 	]*
 [ 	]*11[ 	]+44332211[ 	]*
diff --git a/gas/testsuite/gas/i386/oversized64.l b/gas/testsuite/gas/i386/oversized64.l
index dc63fb5ae77..ac32c4d8139 100644
--- a/gas/testsuite/gas/i386/oversized64.l
+++ b/gas/testsuite/gas/i386/oversized64.l
@@ -1,9 +1,9 @@
 .*: Assembler messages:
-.*:5: Warning: instruction length.*
-.*:6: Warning: instruction length.*
-.*:7: Warning: instruction length.*
-.*:9: Warning: instruction length.*
-.*:10: Warning: instruction length.*
+.*:5: Error: instruction length.*
+.*:6: Error: instruction length.*
+.*:7: Error: instruction length.*
+.*:9: Error: instruction length.*
+.*:10: Error: instruction length.*
 GAS LISTING .*
 
 
@@ -11,29 +11,29 @@ GAS LISTING .*
 [ 	]*2[ 	]+\.intel_syntax noprefix
 [ 	]*3[ 	]+
 [ 	]*4[ 	]+long64:
-[ 	]*5[ 	]+0000 64678FEA[ 	]+lwpins	rax, fs:\[eax\*8\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*5[ 	]+\?\?\?\? 64678FEA[ 	]+lwpins	rax, fs:\[eax\*8\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*5[ 	]+F81204C5[ 	]*
 [ 	]*5[ 	]+00000000[ 	]*
 [ 	]*5[ 	]+44332211[ 	]*
-[ 	]*6[ 	]+0010 64678FEA[ 	]+lwpval	eax, fs:\[eax\*4\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*6[ 	]+\?\?\?\? 64678FEA[ 	]+lwpval	eax, fs:\[eax\*4\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*6[ 	]+78120C85[ 	]*
 [ 	]*6[ 	]+00000000[ 	]*
 [ 	]*6[ 	]+44332211[ 	]*
-[ 	]*7[ 	]+0020 64678FEA[ 	]+bextr	rax, fs:\[eax\*2\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*7[ 	]+\?\?\?\? 64678FEA[ 	]+bextr	rax, fs:\[eax\*2\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*7[ 	]+F8100445[ 	]*
 [ 	]*7[ 	]+00000000[ 	]*
 [ 	]*7[ 	]+44332211[ 	]*
 [ 	]*8[ 	]+
-[ 	]*9[ 	]+0030 6567F2F0[ 	]+xacquire lock add qword ptr gs:\[eax\*8\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*9[ 	]+\?\?\?\? 6567F2F0[ 	]+xacquire lock add qword ptr gs:\[eax\*8\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*9[ 	]+488104C5[ 	]*
 [ 	]*9[ 	]+00000000[ 	]*
 [ 	]*9[ 	]+44332211[ 	]*
-[ 	]*10[ 	]+0040 6567F3F0[ 	]+xrelease lock sub qword ptr gs:\[eax\*8\], 0x11223344
-\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*10[ 	]+\?\?\?\? 6567F3F0[ 	]+xrelease lock sub qword ptr gs:\[eax\*8\], 0x11223344
+\*\*\*\*  Error: instruction length of 16 bytes exceeds the limit of 15
 [ 	]*10[ 	]+48812CC5[ 	]*
 [ 	]*10[ 	]+00000000[ 	]*
 [ 	]*10[ 	]+44332211[ 	]*
diff --git a/gas/testsuite/gas/i386/x86-64-apx-inval.l b/gas/testsuite/gas/i386/x86-64-apx-inval.l
new file mode 100644
index 00000000000..6c1a346fcbf
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-apx-inval.l
@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*:3: Error: instruction length of 16 bytes exceeds the limit of 15
+.*:4: Error: instruction length of 16 bytes exceeds the limit of 15
diff --git a/gas/testsuite/gas/i386/x86-64-apx-inval.s b/gas/testsuite/gas/i386/x86-64-apx-inval.s
new file mode 100644
index 00000000000..bb57817bc8a
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-apx-inval.s
@@ -0,0 +1,4 @@
+# Check illegal 64bit APX_F instructions
+	.text
+	addq $0xe0, %fs:0, %rdx
+	xorq $0xe0, foo(%eax,%edx), %rdx
diff --git a/gas/testsuite/gas/i386/x86-64.exp b/gas/testsuite/gas/i386/x86-64.exp
index 6932ba97a4d..b77e8c10029 100644
--- a/gas/testsuite/gas/i386/x86-64.exp
+++ b/gas/testsuite/gas/i386/x86-64.exp
@@ -371,6 +371,7 @@ run_dump_test "x86-64-avx512f-rcigrne-intel"
 run_dump_test "x86-64-avx512f-rcigrne"
 run_dump_test "x86-64-avx512f-rcigru-intel"
 run_dump_test "x86-64-avx512f-rcigru"
+run_list_test "x86-64-apx-inval"
 run_list_test "x86-64-apx-egpr-inval"
 run_dump_test "x86-64-apx-evex-promoted-bad"
 run_list_test "x86-64-apx-egpr-promote-inval" "-al"