diff --git a/cpu/or1k.opc b/cpu/or1k.opc
index 5d20a1f33a7..748187edcdf 100644
--- a/cpu/or1k.opc
+++ b/cpu/or1k.opc
@@ -38,7 +38,7 @@
 #undef  CGEN_DIS_HASH_SIZE
 #define CGEN_DIS_HASH_SIZE 256
 #undef  CGEN_DIS_HASH
-#define CGEN_DIS_HASH(buffer, value) (((unsigned char *) (buffer))[0] >> 2)
+#define CGEN_DIS_HASH(buffer, value) ((value >> 26) & 0xff)
 
 /* Check applicability of instructions against machines.  */
 #define CGEN_VALIDATE_INSN_SUPPORTED
diff --git a/opcodes/or1k-opc.h b/opcodes/or1k-opc.h
index d3d084b1bec..6eec8006828 100644
--- a/opcodes/or1k-opc.h
+++ b/opcodes/or1k-opc.h
@@ -35,7 +35,7 @@ extern "C" {
 #undef  CGEN_DIS_HASH_SIZE
 #define CGEN_DIS_HASH_SIZE 256
 #undef  CGEN_DIS_HASH
-#define CGEN_DIS_HASH(buffer, value) (((unsigned char *) (buffer))[0] >> 2)
+#define CGEN_DIS_HASH(buffer, value) ((value >> 26) & 0xff)
 
 /* Check applicability of instructions against machines.  */
 #define CGEN_VALIDATE_INSN_SUPPORTED