diff --git a/i386-asm.h b/i386-asm.h
index 16ed5116..0f99b286 100644
--- a/i386-asm.h
+++ b/i386-asm.h
@@ -75,6 +75,9 @@ ALT(DEF_ASM_OP2(btcw, 0x0fba, 7, OPC_MODRM | OPC_WLX, OPT_IM8, OPT_REGW | OPT_EA
 
 ALT(DEF_ASM_OP2(popcntw, 0xf30fb8, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
 
+ALT(DEF_ASM_OP2(tzcntw, 0xf30fbc, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
+ALT(DEF_ASM_OP2(lzcntw, 0xf30fbd, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
+
      /* prefixes */
      DEF_ASM_OP0(wait, 0x9b)
      DEF_ASM_OP0(fwait, 0x9b)
diff --git a/i386-tok.h b/i386-tok.h
index 3145aa63..29071059 100644
--- a/i386-tok.h
+++ b/i386-tok.h
@@ -269,6 +269,8 @@
  DEF_WLX(btr)
  DEF_WLX(btc)
  DEF_WLX(popcnt)
+ DEF_WLX(tzcnt)
+ DEF_WLX(lzcnt)
 
  DEF_WLX(lar)
  DEF_WLX(lsl)
diff --git a/tests/asmtest.S b/tests/asmtest.S
index a2b5d095..7f31ce59 100644
--- a/tests/asmtest.S
+++ b/tests/asmtest.S
@@ -766,7 +766,29 @@ int $0x10
     popcnt %rbx, %rdi
     popcntq %rcx, %r8
 #endif
-        
+
+    lzcnt %cx, %ax
+    lzcntw %cx, %ax
+    lzcnt %edx, %ebx
+    lzcntl 8(%edi), %ecx
+#ifdef __x86_64__
+    lzcnt %rdi, %rdx
+    lzcntq %r12, %r15
+    lzcnt 0x40(%rcx), %r11
+    lzcntq (%r8), %rsi
+#endif
+
+    tzcnt %cx, %ax
+    tzcntw %cx, %ax
+    tzcnt %edx, %ebx
+    tzcntl -24(%edi), %ecx
+#ifdef __x86_64__
+    tzcnt %rbp, %rdx
+    tzcntq %rax, %r15
+    tzcnt -8(%rbp), %rcx
+    tzcntq (%r8), %r12
+#endif
+
 #ifdef __i386__
     boundl %edx, 0x10000
     boundw %bx, 0x1000
diff --git a/x86_64-asm.h b/x86_64-asm.h
index 53b0d30d..339e1dfb 100644
--- a/x86_64-asm.h
+++ b/x86_64-asm.h
@@ -83,6 +83,9 @@ ALT(DEF_ASM_OP2(btcw, 0x0fba, 7, OPC_MODRM | OPC_WLX, OPT_IM8, OPT_REGW | OPT_EA
 
 ALT(DEF_ASM_OP2(popcntw, 0xf30fb8, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
 
+ALT(DEF_ASM_OP2(tzcntw, 0xf30fbc, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
+ALT(DEF_ASM_OP2(lzcntw, 0xf30fbd, 0, OPC_MODRM | OPC_WLX, OPT_REGW | OPT_EA, OPT_REGW))
+
      /* prefixes */
      DEF_ASM_OP0(lock, 0xf0)
      DEF_ASM_OP0(rep, 0xf3)