diff --git a/include/pocketpy/common.h b/include/pocketpy/common.h
index bb612864..9b09c2c3 100644
--- a/include/pocketpy/common.h
+++ b/include/pocketpy/common.h
@@ -187,12 +187,12 @@ struct Type {
 #define PK_ACTION(x) ([](VM* vm, ArgsView args) { x; return vm->None; })
 
 #ifdef POCKETPY_H
-#define FATAL_ERROR() throw std::runtime_error( "L" + std::to_string(__LINE__) + " FATAL_ERROR()!");
+#define PK_FATAL_ERROR() throw std::runtime_error( "L" + std::to_string(__LINE__) + " FATAL_ERROR()!");
 #else
-#define FATAL_ERROR() throw std::runtime_error( __FILE__ + std::string(":") + std::to_string(__LINE__) + " FATAL_ERROR()!");
+#define PK_FATAL_ERROR() throw std::runtime_error( __FILE__ + std::string(":") + std::to_string(__LINE__) + " FATAL_ERROR()!");
 #endif
 
-#define PK_ASSERT(x) if(!(x)) FATAL_ERROR();
+#define PK_ASSERT(x) if(!(x)) PK_FATAL_ERROR();
 
 struct PyObject;
 #define PK_BITS(p) (reinterpret_cast<Number::int_t>(p))
diff --git a/include/pocketpy/frame.h b/include/pocketpy/frame.h
index 647d039d..4f7c5701 100644
--- a/include/pocketpy/frame.h
+++ b/include/pocketpy/frame.h
@@ -59,7 +59,7 @@ struct ValueStackImpl {
     PyObject** end() { return _sp; }
     void reset(PyObject** sp) {
 #if PK_DEBUG_EXTRA_CHECK
-        if(sp < _begin || sp > _begin + MAX_SIZE) FATAL_ERROR();
+        if(sp < _begin || sp > _begin + MAX_SIZE) PK_FATAL_ERROR();
 #endif
         _sp = sp;
     }
@@ -105,7 +105,7 @@ struct Frame {
     Bytecode next_bytecode() {
         _ip = _next_ip++;
 #if PK_DEBUG_EXTRA_CHECK
-        if(_ip >= co->codes.size()) FATAL_ERROR();
+        if(_ip >= co->codes.size()) PK_FATAL_ERROR();
 #endif
         return co->codes[_ip];
     }
diff --git a/include/pocketpy/namedict.h b/include/pocketpy/namedict.h
index e5127a91..3f6026db 100644
--- a/include/pocketpy/namedict.h
+++ b/include/pocketpy/namedict.h
@@ -159,7 +159,7 @@ while(!_items[i].first.empty()) {           \
             if(old_items[i].first.empty()) continue;
             bool ok; uint16_t j;
             HASH_PROBE_1(old_items[i].first, ok, j);
-            if(ok) FATAL_ERROR();
+            if(ok) PK_FATAL_ERROR();
             _items[j] = old_items[i];
         }
         free(old_items);
diff --git a/include/pocketpy/str.h b/include/pocketpy/str.h
index e19df1b6..b8c68e5b 100644
--- a/include/pocketpy/str.h
+++ b/include/pocketpy/str.h
@@ -23,7 +23,7 @@ struct Str{
     Str(int size, bool is_ascii);
     Str(const std::string& s);
     Str(std::string_view s);
-    Str(std::nullptr_t) { FATAL_ERROR(); }
+    Str(std::nullptr_t) { PK_FATAL_ERROR(); }
     Str(const char* s);
     Str(const char* s, int len);
     Str(std::pair<char *, int>);
diff --git a/src/ceval.cpp b/src/ceval.cpp
index 246ca9ea..534be4b7 100644
--- a/src/ceval.cpp
+++ b/src/ceval.cpp
@@ -55,7 +55,7 @@ PyObject* VM::_run_top_frame(){
 
     while(true){
 #if PK_DEBUG_EXTRA_CHECK
-        if(frame.index < base_id) FATAL_ERROR();
+        if(frame.index < base_id) PK_FATAL_ERROR();
 #endif
         try{
             if(need_raise){ need_raise = false; _raise(); }
@@ -845,7 +845,7 @@ __NEXT_STEP:;
 
 #if !PK_ENABLE_COMPUTED_GOTO
         static_assert(OP_DEC_GLOBAL == 111);
-        case 112: case 113: case 114: case 115: case 116: case 117: case 118: case 119: case 120: case 121: case 122: case 123: case 124: case 125: case 126: case 127: case 128: case 129: case 130: case 131: case 132: case 133: case 134: case 135: case 136: case 137: case 138: case 139: case 140: case 141: case 142: case 143: case 144: case 145: case 146: case 147: case 148: case 149: case 150: case 151: case 152: case 153: case 154: case 155: case 156: case 157: case 158: case 159: case 160: case 161: case 162: case 163: case 164: case 165: case 166: case 167: case 168: case 169: case 170: case 171: case 172: case 173: case 174: case 175: case 176: case 177: case 178: case 179: case 180: case 181: case 182: case 183: case 184: case 185: case 186: case 187: case 188: case 189: case 190: case 191: case 192: case 193: case 194: case 195: case 196: case 197: case 198: case 199: case 200: case 201: case 202: case 203: case 204: case 205: case 206: case 207: case 208: case 209: case 210: case 211: case 212: case 213: case 214: case 215: case 216: case 217: case 218: case 219: case 220: case 221: case 222: case 223: case 224: case 225: case 226: case 227: case 228: case 229: case 230: case 231: case 232: case 233: case 234: case 235: case 236: case 237: case 238: case 239: case 240: case 241: case 242: case 243: case 244: case 245: case 246: case 247: case 248: case 249: case 250: case 251: case 252: case 253: case 254: case 255: FATAL_ERROR(); break;
+        case 112: case 113: case 114: case 115: case 116: case 117: case 118: case 119: case 120: case 121: case 122: case 123: case 124: case 125: case 126: case 127: case 128: case 129: case 130: case 131: case 132: case 133: case 134: case 135: case 136: case 137: case 138: case 139: case 140: case 141: case 142: case 143: case 144: case 145: case 146: case 147: case 148: case 149: case 150: case 151: case 152: case 153: case 154: case 155: case 156: case 157: case 158: case 159: case 160: case 161: case 162: case 163: case 164: case 165: case 166: case 167: case 168: case 169: case 170: case 171: case 172: case 173: case 174: case 175: case 176: case 177: case 178: case 179: case 180: case 181: case 182: case 183: case 184: case 185: case 186: case 187: case 188: case 189: case 190: case 191: case 192: case 193: case 194: case 195: case 196: case 197: case 198: case 199: case 200: case 201: case 202: case 203: case 204: case 205: case 206: case 207: case 208: case 209: case 210: case 211: case 212: case 213: case 214: case 215: case 216: case 217: case 218: case 219: case 220: case 221: case 222: case 223: case 224: case 225: case 226: case 227: case 228: case 229: case 230: case 231: case 232: case 233: case 234: case 235: case 236: case 237: case 238: case 239: case 240: case 241: case 242: case 243: case 244: case 245: case 246: case 247: case 248: case 249: case 250: case 251: case 252: case 253: case 254: case 255: PK_FATAL_ERROR(); break;
     }
 #endif
 }
diff --git a/src/compiler.cpp b/src/compiler.cpp
index 0b93abd5..b2e31f0e 100644
--- a/src/compiler.cpp
+++ b/src/compiler.cpp
@@ -299,7 +299,7 @@ namespace pkpy{
             case TK("**"):
                 ctx()->s_expr.push(make_expr<StarredExpr>(2, ctx()->s_expr.popx()));
                 break;
-            default: FATAL_ERROR();
+            default: PK_FATAL_ERROR();
         }
     }
 
@@ -489,7 +489,7 @@ __SUBSCR_END:
         if(is_slice){
             e->b = std::move(slice);
         }else{
-            if(state != 1) FATAL_ERROR();
+            PK_ASSERT(state == 1)
             e->b = std::move(slice->start);
         }
         ctx()->s_expr.push(std::move(e));
@@ -1128,7 +1128,7 @@ __EAT_DOTS_END:
         if(std::holds_alternative<Str>(value)){
             obj = VAR(std::get<Str>(value));
         }
-        if(obj == nullptr) FATAL_ERROR();
+        PK_ASSERT(obj != nullptr)
         return obj;
     }
 
@@ -1163,7 +1163,7 @@ __EAT_DOTS_END:
 
 
     CodeObject_ Compiler::compile(){
-        if(used) FATAL_ERROR();
+        PK_ASSERT(!used)
         used = true;
 
         tokens = lexer->run();
diff --git a/src/expr.cpp b/src/expr.cpp
index ee8036e7..e0e86521 100644
--- a/src/expr.cpp
+++ b/src/expr.cpp
@@ -26,7 +26,7 @@ namespace pkpy{
         if(curr_type == FOR_LOOP) for_loop_depth--;
         co->blocks[curr_block_i].end = co->codes.size();
         curr_block_i = co->blocks[curr_block_i].parent;
-        if(curr_block_i < 0) FATAL_ERROR();
+        if(curr_block_i < 0) PK_FATAL_ERROR();
 
         if(curr_type == FOR_LOOP){
             // add a no op here to make block check work
@@ -116,7 +116,7 @@ namespace pkpy{
             case NAME_GLOBAL_UNKNOWN:
                 emit_(OP_STORE_NAME, StrName(name).index, line);
                 break;
-            default: FATAL_ERROR(); break;
+            default: PK_FATAL_ERROR(); break;
         }
     }
 
@@ -151,7 +151,7 @@ namespace pkpy{
             case NAME_GLOBAL_UNKNOWN:
                 ctx->emit_(OP_DELETE_NAME, StrName(name).index, line);
                 break;
-            default: FATAL_ERROR(); break;
+            default: PK_FATAL_ERROR(); break;
         }
         return true;
     }
@@ -206,7 +206,7 @@ namespace pkpy{
             case TK("True"):    ctx->emit_(OP_LOAD_TRUE, BC_NOARG, line); break;
             case TK("False"):   ctx->emit_(OP_LOAD_FALSE, BC_NOARG, line); break;
             case TK("..."):     ctx->emit_(OP_LOAD_ELLIPSIS, BC_NOARG, line); break;
-            default: FATAL_ERROR();
+            default: PK_FATAL_ERROR();
         }
     }
 
@@ -245,7 +245,7 @@ namespace pkpy{
         if(std::holds_alternative<Str>(value)){
             obj = VAR(std::get<Str>(value));
         }
-        if(obj == nullptr) FATAL_ERROR();
+        PK_ASSERT(obj != nullptr)
         ctx->emit_(OP_LOAD_CONST, ctx->add_const(obj), line);
     }
 
@@ -557,7 +557,7 @@ namespace pkpy{
             if(!kwargs.empty()){
                 for(auto& item: kwargs){
                     if(item.second->is_starred()){
-                        if(item.second->star_level() != 2) FATAL_ERROR();
+                        PK_ASSERT(item.second->star_level() == 2)
                         item.second->emit_(ctx);
                     }else{
                         // k=v
@@ -658,7 +658,7 @@ namespace pkpy{
             case TK("^"):   ctx->emit_(OP_BITWISE_XOR, BC_NOARG, line);  break;
 
             case TK("@"):   ctx->emit_(OP_BINARY_MATMUL, BC_NOARG, line);  break;
-            default: FATAL_ERROR();
+            default: PK_FATAL_ERROR();
         }
 
         for(int i: jmps) ctx->patch_jump(i);
diff --git a/src/gc.cpp b/src/gc.cpp
index 9831c5a3..5c1daf7d 100644
--- a/src/gc.cpp
+++ b/src/gc.cpp
@@ -41,7 +41,7 @@ namespace pkpy{
     }
 
     int ManagedHeap::collect(){
-        if(_gc_lock_counter > 0) FATAL_ERROR();
+        PK_ASSERT(_gc_lock_counter == 0)
         mark();
         int freed = sweep();
         return freed;
diff --git a/src/lexer.cpp b/src/lexer.cpp
index 2510669a..4eb6a495 100644
--- a/src/lexer.cpp
+++ b/src/lexer.cpp
@@ -438,7 +438,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
                         case 2: SyntaxError("invalid utf8 sequence: " + std::string(1, c)); break;
                         case 3: SyntaxError("@id contains invalid char"); break;
                         case 4: SyntaxError("invalid JSON token"); break;
-                        default: FATAL_ERROR();
+                        default: PK_FATAL_ERROR();
                     }
                     return true;
                 }
@@ -473,7 +473,7 @@ static bool is_unicode_Lo_char(uint32_t c) {
     }
 
     std::vector<Token> Lexer::run() {
-        if(used) FATAL_ERROR();
+        PK_ASSERT(!used)
         used = true;
         while (lex_one_token());
         return std::move(nexts);
diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 4bc25577..7ccf0ff8 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -276,7 +276,7 @@ void init_builtins(VM* _vm) {
     });
 
     _vm->bind__repr__(_vm->tp_object, [](VM* vm, PyObject* obj) {
-        if(is_tagged(obj)) FATAL_ERROR();
+        if(is_tagged(obj)) PK_FATAL_ERROR();
         std::stringstream ss; // hex
         ss << "<" << OBJ_NAME(vm->_t(obj)) << " object at 0x";
         ss << std::hex << reinterpret_cast<intptr_t>(obj) << ">";
diff --git a/src/vm.cpp b/src/vm.cpp
index ae627094..587482f7 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -121,7 +121,7 @@ namespace pkpy{
 
     FrameId VM::top_frame(){
 #if PK_DEBUG_EXTRA_CHECK
-        if(callstack.empty()) FATAL_ERROR();
+        if(callstack.empty()) PK_FATAL_ERROR();
 #endif
         return FrameId(&callstack.data(), callstack.size()-1);
     }
@@ -240,7 +240,7 @@ namespace pkpy{
         PyObject* obj = builtins->attr().try_get_likely_found(type);
         if(obj == nullptr){
             for(auto& t: _all_types) if(t.name == type) return &t;
-            FATAL_ERROR();
+            PK_FATAL_ERROR();
         }
         return &_all_types[PK_OBJ_GET(Type, obj)];
     }
@@ -669,7 +669,7 @@ void VM::_log_s_data(const char* title) {
     if(title) ss << title << " | ";
     std::map<PyObject**, int> sp_bases;
     for(Frame& f: callstack.data()){
-        if(f._sp_base == nullptr) FATAL_ERROR();
+        if(f._sp_base == nullptr) PK_FATAL_ERROR();
         sp_bases[f._sp_base] += 1;
     }
     FrameId frame = top_frame();
@@ -877,7 +877,7 @@ PyObject* VM::vectorcall(int ARGC, int KWARGC, bool op_call){
 
     // handle boundmethod, do a patch
     if(is_non_tagged_type(callable, tp_bound_method)){
-        if(method_call) FATAL_ERROR();
+        if(method_call) PK_FATAL_ERROR();
         auto& bm = CAST(BoundMethod&, callable);
         callable = bm.func;      // get unbound method
         p1[-(ARGC + 2)] = bm.func;
@@ -962,7 +962,7 @@ __FAST_CALL:
     }
 
     if(is_non_tagged_type(callable, tp_type)){
-        if(method_call) FATAL_ERROR();
+        if(method_call) PK_FATAL_ERROR();
         // [type, NULL, args..., kwargs...]
         PyObject* new_f = find_name_in_mro(callable, __new__);
         PyObject* obj;