diff --git a/src/cheat.c b/src/cheat.c
index 2602bf5..cdf0aaf 100644
--- a/src/cheat.c
+++ b/src/cheat.c
@@ -332,33 +332,27 @@ int FCEUI_DecodeGG(const char *str, uint16 *a, uint8 *v, int *c) {
 	if (s != 6 && s != 8) return(0);
 
 	t = GGtobin(*str++);
-	if (!t) return (0);
 	V |= (t & 0x07);
 	V |= (t & 0x08) << 4;
 
 	t = GGtobin(*str++);
-	if (!t) return (0);
 	V |= (t & 0x07) << 4;
 	A |= (t & 0x08) << 4;
 
 	t = GGtobin(*str++);
-	if (!t) return (0);
 	A |= (t & 0x07) << 4;
 	/* if(t&0x08) return(0); */  /* 8-character code?! */
 
 	t = GGtobin(*str++);
-	if (!t) return (0);
 	A |= (t & 0x07) << 12;
 	A |= (t & 0x08);
 
 	t = GGtobin(*str++);
-	if (!t) return (0);
 	A |= (t & 0x07);
 	A |= (t & 0x08) << 8;
 
 	if (s == 6) {
 		t = GGtobin(*str++);
-		if (!t) return (0);
 		A |= (t & 0x07) << 8;
 		V |= (t & 0x08);
 
@@ -368,17 +362,14 @@ int FCEUI_DecodeGG(const char *str, uint16 *a, uint8 *v, int *c) {
 		return(1);
 	} else {
 		t = GGtobin(*str++);
-		if (!t) return (0);
 		A |= (t & 0x07) << 8;
 		C |= (t & 0x08);
 
 		t = GGtobin(*str++);
-		if (!t) return (0);
 		C |= (t & 0x07);
 		C |= (t & 0x08) << 4;
 
 		t = GGtobin(*str++);
-		if (!t) return (0);
 		C |= (t & 0x07) << 4;
 		V |= (t & 0x08);
 		*a = A;
diff --git a/src/drivers/libretro/libretro.c b/src/drivers/libretro/libretro.c
index 25209c3..5aa8526 100644
--- a/src/drivers/libretro/libretro.c
+++ b/src/drivers/libretro/libretro.c
@@ -3,6 +3,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdarg.h>
+#include <ctype.h>
 
 #include <libretro.h>
 #include <streams/memory_stream.h>
@@ -1958,6 +1959,31 @@ bool retro_unserialize(const void * data, size_t size)
    return true;
 }
 
+static int checkGG(char c)
+{
+   static const char lets[16] = { 'A', 'P', 'Z', 'L', 'G', 'I', 'T', 'Y', 'E', 'O', 'X', 'U', 'K', 'S', 'V', 'N' };
+   int x;
+
+   for (x = 0; x < 16; x++)
+      if (lets[x] == toupper(c))
+         return 1;
+   return 0;
+}
+
+static int GGisvalid(const char *code)
+{
+   size_t len = strlen(code);
+   int i;
+   
+   if (len != 6 && len != 8)
+      return 0;
+
+   for (i = 0; i < len; i++)
+      if (!checkGG(code[i]))
+         return 0;
+   return 1;
+}
+
 void retro_cheat_reset(void)
 {
    FCEU_ResetCheats();
@@ -2010,7 +2036,7 @@ void retro_cheat_set(unsigned index, bool enabled, const char *code)
          if (a < 0x0100) type = 0;
          FCEUI_AddCheat(name, a, v, c, type);
       }
-      else if (FCEUI_DecodeGG(codepart, &a, &v, &c))
+      else if (GGisvalid(codepart) && FCEUI_DecodeGG(codepart, &a, &v, &c))
       {
          FCEUI_AddCheat(name, a, v, c, type);
          log_cb.log(RETRO_LOG_DEBUG, "Cheat code added: '%s' (GG)\n", codepart);
@@ -2020,6 +2046,8 @@ void retro_cheat_set(unsigned index, bool enabled, const char *code)
          FCEUI_AddCheat(name, a, v, c, type);
          log_cb.log(RETRO_LOG_DEBUG, "Cheat code added: '%s' (PAR)\n", codepart);
       }
+      else
+         log_cb.log(RETRO_LOG_DEBUG, "Invalid or unknown code: '%s'\n", codepart);
       codepart = strtok(NULL,"+,;._ ");
    }
 }