diff --git a/encode-test.inc b/encode-test.inc
index 7113717..6cc06ee 100644
--- a/encode-test.inc
+++ b/encode-test.inc
@@ -130,6 +130,9 @@ TEST("", SSE_PEXTRBrri, 0, FE_CH, FE_XMM0, 2);
 #endif
 TEST("\x66\x0f\xf7\xc1", SSE_MASKMOVDQUrr, 0, FE_XMM0, FE_XMM1);
 TEST("\x67\x66\x0f\xf7\xc1", SSE_MASKMOVDQUrr, FE_ADDR32, FE_XMM0, FE_XMM1);
+TEST("\x0f\xae\xe8", LFENCE, 0);
+TEST("\x0f\xae\xf0", MFENCE, 0);
+TEST("\x0f\xae\xf8", SFENCE, 0);
 
 // Test FD/TD encodings
 TEST("\xa0\x00\x00\x00\x00\x00\x00\x00\x00", MOV8ra, 0, FE_AX, 0);
diff --git a/instrs.txt b/instrs.txt
index 8c53728..5f37e0f 100644
--- a/instrs.txt
+++ b/instrs.txt
@@ -731,9 +731,9 @@ NP.0fae/0m             M    M   -   -   -   FXSAVE+w            F=FXSR
 NP.0fae/1m             M    M   -   -   -   FXRSTOR+w           F=FXSR
 NP.0fae/2m             M    Md  -   -   -   LDMXCSR             F=SSE
 NP.0fae/3m             M    Md  -   -   -   STMXCSR             F=SSE
-NP.0fae/5r             NP   -   -   -   -   LFENCE              F=SSE2
-NP.0fae/6r             NP   -   -   -   -   MFENCE              F=SSE2
-NP.0fae/7r             NP   -   -   -   -   SFENCE              F=SSE
+NP.0faee8+             NP   -   -   -   -   LFENCE              F=SSE2
+NP.0faef0+             NP   -   -   -   -   MFENCE              F=SSE2
+NP.0faef8+             NP   -   -   -   -   SFENCE              F=SSE
 NP.0fc2                RMI  Vps Wps Ib  -   SSE_CMPPS           F=SSE
 66.0fc2                RMI  Vpd Wpd Ib  -   SSE_CMPPD           F=SSE2
 F3.0fc2                RMI  Vss Wss Ib  -   SSE_CMPSS           F=SSE
diff --git a/parseinstrs.py b/parseinstrs.py
index 2d1e3c8..eeae4b4 100644
--- a/parseinstrs.py
+++ b/parseinstrs.py
@@ -326,7 +326,7 @@ opcode_regex = re.compile(
                      r"(?:W(?P<rexw>[01]|IG)\.)?(?:L(?P<vexl>[01]|IG)\.)?))?" +
      r"(?P<escape>0f38|0f3a|0f|)" +
      r"(?P<opcode>[0-9a-f]{2})" +
-     r"(?:(?P<extended>\+)|/(?P<modreg>[0-7]|[rm]|[0-7][rm])|(?P<opcext>[c-f][0-9a-f]))?$")
+     r"(?:/(?P<modreg>[0-7]|[rm]|[0-7][rm])|(?P<opcext>[c-f][0-9a-f]))?(?P<extended>\+)?$")
 
 class Opcode(NamedTuple):
     prefix: Union[None, str] # None/NP/66/F2/F3/NFx
@@ -397,7 +397,7 @@ class Trie:
 
     def _transform_opcode(self, opc):
         troot = [opc.escape | opc.vex << 2]
-        t256 = [opc.opc + i for i in range(8 if opc.extended else 1)]
+        t256 = [opc.opc + i for i in range(8 if opc.extended and not opc.opcext else 1)]
         tprefix, t16, t8e, tvex = None, None, None, None
         if opc.prefix == "NFx":
             tprefix = [0, 1]
@@ -405,7 +405,8 @@ class Trie:
             tprefix = [["NP", "66", "F3", "F2"].index(opc.prefix)]
         if opc.opcext:
             t16 = [((opc.opcext - 0xc0) >> 3) | 8]
-            t8e = [opc.opcext & 7]
+            if not opc.extended:
+                t8e = [opc.opcext & 7]
         elif opc.modreg:
             # TODO: optimize for /r and /m specifiers to reduce size
             mod = {"m": [0], "r": [1<<3], "rm": [0, 1<<3]}[opc.modreg[1]]