diff --git a/src/i_system.h b/src/i_system.h
index 0dbd1412..9c601d54 100644
--- a/src/i_system.h
+++ b/src/i_system.h
@@ -58,7 +58,7 @@ ticcmd_t* I_BaseTiccmd (void);
 
 // killough 3/20/98: add const
 // killough 4/25/98: add gcc attributes
-void I_ErrorOrSuccess(int err_code, const char *error, ...) PRINTF_ATTR(2, 3);
+void I_ErrorOrSuccess(int err_code, const char *error, ...) NORETURN PRINTF_ATTR(2, 3);
 #define I_Error(...) I_ErrorOrSuccess(-1, __VA_ARGS__)
 #define I_Success(...) I_ErrorOrSuccess(0, __VA_ARGS__)