diff --git a/src/VM/VM.h b/src/VM/VM.h
index a141f27..5b54297 100644
--- a/src/VM/VM.h
+++ b/src/VM/VM.h
@@ -45,7 +45,7 @@ typedef struct VM {
     };
     
     VMState state;
-    char* error_message;
+    NULLABLE(char* error_message);
 
     u8* data;
     size_t data_size;
diff --git a/src/instructions/impl/SYS.c b/src/instructions/impl/SYS.c
index 1a9e651..825b81e 100644
--- a/src/instructions/impl/SYS.c
+++ b/src/instructions/impl/SYS.c
@@ -1,6 +1,6 @@
 #include "impl_macros.h"
 
-FILE* fileFromN(VM* vm, size_t pos, u32 file_n){
+NULLABLE(FILE* fileFromN(VM* vm, size_t pos, u32 file_n)){
     FILE* f = NULL;
     switch(file_n){
         case 0: f = stdin; break;
diff --git a/src/instructions/instructions.c b/src/instructions/instructions.c
index bb4f01b..871f09a 100644
--- a/src/instructions/instructions.c
+++ b/src/instructions/instructions.c
@@ -16,7 +16,7 @@ const Instruction instructions[] = {
 };
 const size_t instructions_count = sizeof(instructions)/sizeof(instructions[0]);
 
-const Instruction* Instruction_getFromOpcode(u8 opcode){
+NULLABLE(const Instruction* Instruction_getFromOpcode(u8 opcode)){
     if(opcode >= instructions_count)
         return NULL;
     
diff --git a/src/instructions/instructions.h b/src/instructions/instructions.h
index a720861..332ae40 100644
--- a/src/instructions/instructions.h
+++ b/src/instructions/instructions.h
@@ -18,7 +18,7 @@ typedef struct Instruction {
 /// @brief get instruction info from table
 /// @param opcode any byte
 /// @return ptr to struct or NULL
-const Instruction* Instruction_getFromOpcode(u8 opcode);
+NULLABLE(const Instruction* Instruction_getFromOpcode(u8 opcode));
 
 i32 NOP_impl(VM* vm, size_t pos);
 i32 PUSH_impl(VM* vm, size_t pos);
diff --git a/src/main.c b/src/main.c
index e657940..b83f590 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4,7 +4,7 @@
 #define arg_is(STR) (strcmp(argv[argi], STR) == 0)
 
 i32 main(const i32 argc, const char** argv){
-    const char* filename = NULL;
+    const char* NULLABLE(filename) = NULL;
 
     for(i32 argi = 1; argi < argc; argi++){
         if(arg_is("-h") || arg_is("--help")){
diff --git a/src/std.h b/src/std.h
index d3321cc..2ac9d64 100644
--- a/src/std.h
+++ b/src/std.h
@@ -24,4 +24,7 @@ typedef u8 bool;
 #define true  1
 #define false 0
 
-#define printfe(FORMAT, ...) fprintf(stderr, FORMAT ,##__VA_ARGS__)
\ No newline at end of file
+#define printfe(FORMAT, ...) fprintf(stderr, FORMAT ,##__VA_ARGS__)
+
+/// @warning pointer can be null
+#define NULLABLE(DECLARATION) DECLARATION