diff --git a/modules/arch/x86/tests/Makefile.inc b/modules/arch/x86/tests/Makefile.inc
index 60406bfc..c513ad17 100644
--- a/modules/arch/x86/tests/Makefile.inc
+++ b/modules/arch/x86/tests/Makefile.inc
@@ -84,6 +84,8 @@ EXTRA_DIST += modules/arch/x86/tests/mem64hi32.asm
 EXTRA_DIST += modules/arch/x86/tests/mem64hi32.hex
 EXTRA_DIST += modules/arch/x86/tests/mem64rip.asm
 EXTRA_DIST += modules/arch/x86/tests/mem64rip.hex
+EXTRA_DIST += modules/arch/x86/tests/mixcase.asm
+EXTRA_DIST += modules/arch/x86/tests/mixcase.hex
 EXTRA_DIST += modules/arch/x86/tests/movdq32.asm
 EXTRA_DIST += modules/arch/x86/tests/movdq32.hex
 EXTRA_DIST += modules/arch/x86/tests/movdq64.asm
diff --git a/modules/arch/x86/tests/mixcase.asm b/modules/arch/x86/tests/mixcase.asm
new file mode 100644
index 00000000..4964e721
--- /dev/null
+++ b/modules/arch/x86/tests/mixcase.asm
@@ -0,0 +1,3 @@
+CPU SSE5
+MOV AX,5
+
diff --git a/modules/arch/x86/tests/mixcase.hex b/modules/arch/x86/tests/mixcase.hex
new file mode 100644
index 00000000..76dc00b9
--- /dev/null
+++ b/modules/arch/x86/tests/mixcase.hex
@@ -0,0 +1,3 @@
+b8 
+05 
+00 
diff --git a/modules/arch/x86/x86cpu.gperf b/modules/arch/x86/x86cpu.gperf
index 3597b535..5878a917 100644
--- a/modules/arch/x86/x86cpu.gperf
+++ b/modules/arch/x86/x86cpu.gperf
@@ -332,12 +332,16 @@ yasm_x86__parse_cpu(yasm_arch_x86 *arch_x86, const char *cpuid,
 {
     /*@null@*/ const struct cpu_parse_data *pdata;
     wordptr new_cpu;
-    unsigned int i;
+    size_t i;
+    static char lcaseid[16];
 
     if (cpuid_len > 15)
         return;
+    for (i=0; i<cpuid_len; i++)
+        lcaseid[i] = tolower(cpuid[i]);
+    lcaseid[cpuid_len] = '\0';
 
-    pdata = cpu_find(cpuid, cpuid_len);
+    pdata = cpu_find(lcaseid, cpuid_len);
     if (!pdata) {
         yasm_warn_set(YASM_WARN_GENERAL,
                       N_("unrecognized CPU identifier `%s'"), cpuid);
diff --git a/modules/arch/x86/x86regtmod.gperf b/modules/arch/x86/x86regtmod.gperf
index e9d2ac9c..e3d0a89e 100644
--- a/modules/arch/x86/x86regtmod.gperf
+++ b/modules/arch/x86/x86regtmod.gperf
@@ -241,13 +241,18 @@ yasm_x86__parse_check_regtmod(yasm_arch *arch, const char *id, size_t id_len,
 {
     yasm_arch_x86 *arch_x86 = (yasm_arch_x86 *)arch;
     /*@null@*/ const struct regtmod_parse_data *pdata;
+    size_t i;
+    static char lcaseid[8];
     unsigned int bits;
     yasm_arch_regtmod type;
 
     if (id_len > 7)
         return YASM_ARCH_NOTREGTMOD;
+    for (i=0; i<id_len; i++)
+        lcaseid[i] = tolower(id[i]);
+    lcaseid[id_len] = '\0';
 
-    pdata = regtmod_find(id, id_len);
+    pdata = regtmod_find(lcaseid, id_len);
     if (!pdata)
         return YASM_ARCH_NOTREGTMOD;