diff --git a/dlls/ole32/compobj.c b/dlls/ole32/compobj.c
index 719d9de5f5f..e615599fc93 100644
--- a/dlls/ole32/compobj.c
+++ b/dlls/ole32/compobj.c
@@ -2065,11 +2065,21 @@ static inline BOOL is_valid_hex(WCHAR c)
     return TRUE;
 }
 
+static const BYTE guid_conv_table[256] =
+{
+  0,   0,   0,   0,   0,   0,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x00 */
+  0,   0,   0,   0,   0,   0,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x10 */
+  0,   0,   0,   0,   0,   0,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x20 */
+  0,   1,   2,   3,   4,   5,   6, 7, 8, 9, 0, 0, 0, 0, 0, 0, /* 0x30 */
+  0, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x40 */
+  0,   0,   0,   0,   0,   0,   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x50 */
+  0, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf                             /* 0x60 */
+};
+
 /* conversion helper for CLSIDFromString/IIDFromString */
 static BOOL guid_from_string(LPCWSTR s, GUID *id)
 {
   int	i;
-  BYTE table[256];
 
   if (!s || s[0]!='{') {
     memset( id, 0, sizeof (CLSID) );
@@ -2079,37 +2089,26 @@ static BOOL guid_from_string(LPCWSTR s, GUID *id)
 
   TRACE("%s -> %p\n", debugstr_w(s), id);
 
-  /* quick lookup table */
-  memset(table, 0, 256);
-
-  for (i = 0; i < 10; i++) {
-    table['0' + i] = i;
-  }
-  for (i = 0; i < 6; i++) {
-    table['A' + i] = i+10;
-    table['a' + i] = i+10;
-  }
-
   /* in form {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} */
 
   id->Data1 = 0;
   for (i = 1; i < 9; i++) {
     if (!is_valid_hex(s[i])) return FALSE;
-    id->Data1 = (id->Data1 << 4) | table[s[i]];
+    id->Data1 = (id->Data1 << 4) | guid_conv_table[s[i]];
   }
   if (s[9]!='-') return FALSE;
 
   id->Data2 = 0;
   for (i = 10; i < 14; i++) {
     if (!is_valid_hex(s[i])) return FALSE;
-    id->Data2 = (id->Data2 << 4) | table[s[i]];
+    id->Data2 = (id->Data2 << 4) | guid_conv_table[s[i]];
   }
   if (s[14]!='-') return FALSE;
 
   id->Data3 = 0;
   for (i = 15; i < 19; i++) {
     if (!is_valid_hex(s[i])) return FALSE;
-    id->Data3 = (id->Data3 << 4) | table[s[i]];
+    id->Data3 = (id->Data3 << 4) | guid_conv_table[s[i]];
   }
   if (s[19]!='-') return FALSE;
 
@@ -2119,7 +2118,7 @@ static BOOL guid_from_string(LPCWSTR s, GUID *id)
       i++;
     }
     if (!is_valid_hex(s[i]) || !is_valid_hex(s[i+1])) return FALSE;
-    id->Data4[(i-20)/2] = table[s[i]] << 4 | table[s[i+1]];
+    id->Data4[(i-20)/2] = guid_conv_table[s[i]] << 4 | guid_conv_table[s[i+1]];
   }
 
   if (s[37] == '}' && s[38] == '\0')