diff --git a/src/cpu/core_dyn_x86.cpp b/src/cpu/core_dyn_x86.cpp
index 3ed19175..07bfa63e 100644
--- a/src/cpu/core_dyn_x86.cpp
+++ b/src/cpu/core_dyn_x86.cpp
@@ -147,8 +147,8 @@ static struct {
 	Bitu ea,tmpb,tmpd,stack,shift;
 } extra_regs;
 
-static void IllegalOption(void) {
-	E_Exit("Illegal option");
+static void IllegalOption(const char* msg) {
+	E_Exit("DynCore: illegal option in %s",msg);
 }
 
 #include "core_dyn_x86/cache.h" 
diff --git a/src/cpu/core_dyn_x86/decoder.h b/src/cpu/core_dyn_x86/decoder.h
index 9733b1e8..c0c53e01 100644
--- a/src/cpu/core_dyn_x86/decoder.h
+++ b/src/cpu/core_dyn_x86/decoder.h
@@ -832,14 +832,14 @@ static void dyn_load_seg_off_ea(SegNames seg) {
 		dyn_load_seg(seg,DREG(TMPW));gen_releasereg(DREG(TMPW));
 		dyn_read_word_release(DREG(EA),&DynRegs[decode.modrm.reg],decode.big_op);
 	} else {
-		IllegalOption();
+		IllegalOption("dyn_load_seg_off_ea");
 	}
 }
 
 static void dyn_mov_seg_ev(void) {
 	dyn_get_modrm();
 	SegNames seg=(SegNames)decode.modrm.reg;
-	if (GCC_UNLIKELY(seg==cs)) IllegalOption();
+	if (GCC_UNLIKELY(seg==cs)) IllegalOption("dyn_mov_seg_ev");
 	if (decode.modrm.mod<3) {
 		dyn_fill_ea();
 		dyn_read_word(DREG(EA),DREG(EA),false);
@@ -905,7 +905,7 @@ static void dyn_leave(void) {
 }
 
 static void dyn_segprefix(SegNames seg) {
-	if (GCC_UNLIKELY((Bitu)(decode.segprefix))) IllegalOption();
+	if (GCC_UNLIKELY((Bitu)(decode.segprefix))) IllegalOption("dyn_segprefix");
 	decode.segprefix=&DynRegs[G_ES+seg];
 }
 
@@ -1645,7 +1645,7 @@ restart_prefix:
 				dyn_push(src);
 				break;
 			default:
-				IllegalOption();
+				IllegalOption("opcode 0xff");
 			}}
 			break;
 		default:
diff --git a/src/cpu/core_dyn_x86/risc_x86.h b/src/cpu/core_dyn_x86/risc_x86.h
index f656e547..11430f1b 100644
--- a/src/cpu/core_dyn_x86/risc_x86.h
+++ b/src/cpu/core_dyn_x86/risc_x86.h
@@ -61,7 +61,7 @@ public:
 		dynreg->flags|=DYNFLG_ACTIVE;
 	}
 	void Save(void) {
-		if (GCC_UNLIKELY(!((Bitu)dynreg))) IllegalOption();
+		if (GCC_UNLIKELY(!((Bitu)dynreg))) IllegalOption("GenReg->Save");
 		dynreg->flags&=~DYNFLG_CHANGED;
 		cache_addw(0x0589+(index << (8+3)));		//Mov [data],reg
 		cache_addd((Bit32u)dynreg->data);
@@ -283,7 +283,7 @@ static void gen_dop_byte(DualOps op,DynReg * dr1,Bit8u di1,DynReg * dr2,Bit8u di
 	case DOP_MOV:	if ((dr1==dr2) && (di1==di2)) return; tmp=0x8a; break;
 	case DOP_XCHG:	tmp=0x86; dr2->flags|=DYNFLG_CHANGED; break;
 	default:
-		IllegalOption();
+		IllegalOption("gen_dop_byte");
 	}
 	dr1->flags|=DYNFLG_CHANGED;
 nochange:
@@ -307,7 +307,7 @@ static void gen_dop_byte_imm(DualOps op,DynReg * dr1,Bit8u di1,Bitu imm) {
 					dr1->flags|=DYNFLG_CHANGED;
 					goto finish;
 	default:
-		IllegalOption();
+		IllegalOption("gen_dop_byte_imm");
 	}
 	dr1->flags|=DYNFLG_CHANGED;
 nochange:
@@ -325,7 +325,7 @@ static void gen_sop_byte(SingleOps op,DynReg * dr1,Bit8u di1) {
 	case SOP_NOT: tmp=0xd0f6; break;
 	case SOP_NEG: tmp=0xd8f6; break;
 	default:
-		IllegalOption();
+		IllegalOption("gen_sop_byte");
 	}
 	cache_addw(tmp + ((gr1->index+di1)<<8));
 	dr1->flags|=DYNFLG_CHANGED;
@@ -423,7 +423,7 @@ static void gen_dop_word(DualOps op,bool dword,DynReg * dr1,DynReg * dr2) {
 		tmp=0x87;
 		break;
 	default:
-		IllegalOption();
+		IllegalOption("gen_dop_word");
 	}
 	dr1->flags|=DYNFLG_CHANGED;
 nochange:
@@ -447,7 +447,7 @@ static void gen_dop_word_imm(DualOps op,bool dword,DynReg * dr1,Bits imm) {
 	case DOP_TEST:	tmp=0xc0f7; goto nochange;	//Doesn't change
 	case DOP_MOV:	cache_addb(0xb8+(gr1->index)); dr1->flags|=DYNFLG_CHANGED; goto finish;
 	default:
-		IllegalOption();
+		IllegalOption("gen_dop_word_imm");
 	}
 	dr1->flags|=DYNFLG_CHANGED;
 nochange:
@@ -494,7 +494,7 @@ static void gen_sop_word(SingleOps op,bool dword,DynReg * dr1) {
 	case SOP_NOT:cache_addw(0xd0f7+(gr1->index<<8));break;
 	case SOP_NEG:cache_addw(0xd8f7+(gr1->index<<8));break;
 	default:
-		IllegalOption();
+		IllegalOption("gen_sop_word");
 	}
 	dr1->flags|=DYNFLG_CHANGED;
 }
@@ -654,7 +654,7 @@ static void gen_call_function(void * func,char * ops,...) {
 						release=true;
 						goto scanagain;
 					default:
-						IllegalOption();
+						IllegalOption("gen_call_function param:DREG");
 					}
 					if (release) gen_releasereg(dynreg);
 				}
@@ -664,7 +664,7 @@ static void gen_call_function(void * func,char * ops,...) {
 				pinfo[pindex].line=scan;
 				break;
 			default:
-				IllegalOption();
+				IllegalOption("gen_call_function unknown param");
 			}
 		}
 	}
@@ -725,7 +725,7 @@ static void gen_call_write(DynReg * dr,Bit32u val,Bitu write_size) {
 		case 1: cache_addd((Bit32u)mem_writeb - (Bit32u)cache.pos-4); break;
 		case 2: cache_addd((Bit32u)mem_writew_dyncorex86 - (Bit32u)cache.pos-4); break;
 		case 4: cache_addd((Bit32u)mem_writed_dyncorex86 - (Bit32u)cache.pos-4); break;
-		default: IllegalOption();
+		default: IllegalOption("gen_call_write");
 	}
 
 	cache_addw(0xc483);		//ADD ESP,8
@@ -777,7 +777,7 @@ static void gen_jmp_ptr(void * ptr,Bits imm=0) {
 }
 
 static void gen_save_flags(DynReg * dynreg) {
-	if (GCC_UNLIKELY(x86gen.flagsactive)) IllegalOption();
+	if (GCC_UNLIKELY(x86gen.flagsactive)) IllegalOption("gen_save_flags");
 	GenReg * genreg=FindDynReg(dynreg);
 	cache_addb(0x8b);					//MOV REG,[esp]
 	cache_addw(0x2404+(genreg->index << 3));
@@ -785,7 +785,7 @@ static void gen_save_flags(DynReg * dynreg) {
 }
 
 static void gen_load_flags(DynReg * dynreg) {
-	if (GCC_UNLIKELY(x86gen.flagsactive)) IllegalOption();
+	if (GCC_UNLIKELY(x86gen.flagsactive)) IllegalOption("gen_load_flags");
 	cache_addw(0xc483);				//ADD ESP,4
 	cache_addb(0x4);
 	GenReg * genreg=FindDynReg(dynreg);
@@ -805,7 +805,7 @@ static void gen_load_host(void * data,DynReg * dr1,Bitu size) {
 	case 2:cache_addw(0xb70f);break;	//movzx word
 	case 4:cache_addb(0x8b);break;	//mov
 	default:
-		IllegalOption();
+		IllegalOption("gen_load_host");
 	}
 	cache_addb(0x5+(gr1->index<<3));
 	cache_addd((Bit32u)data);
diff --git a/src/cpu/core_dyn_x86/string.h b/src/cpu/core_dyn_x86/string.h
index e59c7077..4c8a710c 100644
--- a/src/cpu/core_dyn_x86/string.h
+++ b/src/cpu/core_dyn_x86/string.h
@@ -51,7 +51,7 @@ static void dyn_string(STRING_OP op) {
 	case STR_INSB:	case STR_INSW:	case STR_INSD:
 		tmp_reg=DREG(TMPB);usesi=false;usedi=true;break;
 	default:
-		IllegalOption();
+		IllegalOption("dyn_string op");
 	}
 	gen_load_host(&cpu.direction,DREG(TMPW),4);
 	switch (op & 3) {
@@ -59,7 +59,7 @@ static void dyn_string(STRING_OP op) {
 	case 1:gen_shift_word_imm(SHIFT_SHL,true,DREG(TMPW),1);break;
 	case 2:gen_shift_word_imm(SHIFT_SHL,true,DREG(TMPW),2);break;
 	default:
-		IllegalOption();
+		IllegalOption("dyn_string shift");
 
 	}
 	if (usesi) {
@@ -139,7 +139,7 @@ static void dyn_string(STRING_OP op) {
 			dyn_write_word(DREG(EA),tmp_reg,true);
 			break;
 		default:
-			IllegalOption();
+			IllegalOption("dyn_string op");
 		}
 	}
 	gen_releasereg(DREG(EA));gen_releasereg(DREG(TMPB));