diff --git a/src/Decoder.c b/src/Decoder.c
index cd04854..0d4a710 100644
--- a/src/Decoder.c
+++ b/src/Decoder.c
@@ -905,7 +905,7 @@ static uint8_t ZydisCalcRegisterId(ZydisDecoderContext* context, ZydisInstructio
         case ZYDIS_REG_ENCODING_REG:
         {
             ZYDIS_ASSERT(info->details.modrm.isDecoded);
-            uint8_t value = info->details.modrm.reg | (context->cache.R << 3);
+            uint8_t value = info->details.modrm.reg;
             // R' only exists for EVEX and MVEX. No encoding check needed
             switch (registerClass)
             {
@@ -914,7 +914,10 @@ static uint8_t ZydisCalcRegisterId(ZydisDecoderContext* context, ZydisInstructio
             case ZYDIS_REGCLASS_ZMM:              
                 value |= (context->cache.R2 << 4);
                 break;
+            case ZYDIS_REGCLASS_MASK:
+                break;
             default:
+                value |= (context->cache.R  << 3);
                 break;
             }
             return value;
@@ -935,7 +938,7 @@ static uint8_t ZydisCalcRegisterId(ZydisDecoderContext* context, ZydisInstructio
         case ZYDIS_REG_ENCODING_RM:
         {
             ZYDIS_ASSERT(info->details.modrm.isDecoded);
-            uint8_t value = info->details.modrm.rm | (context->cache.B << 3);
+            uint8_t value = info->details.modrm.rm;
             // We have to check the instruction-encoding, because the extension by X is only valid
             // for EVEX and MVEX instructions
             if ((info->encoding == ZYDIS_INSTRUCTION_ENCODING_EVEX) ||
@@ -948,7 +951,10 @@ static uint8_t ZydisCalcRegisterId(ZydisDecoderContext* context, ZydisInstructio
                 case ZYDIS_REGCLASS_ZMM:
                     value |= (context->cache.X << 4);
                     break;
+                case ZYDIS_REGCLASS_MASK:
+                    break;
                 default:
+                    value |= (context->cache.B << 3);
                     break;
                 }
             }