diff --git a/kitty/data-types.h b/kitty/data-types.h
index cc9589b98..a6b5609b7 100644
--- a/kitty/data-types.h
+++ b/kitty/data-types.h
@@ -27,7 +27,7 @@
 #define xstr(s) str(s)
 #define str(s) #s
 #define arraysz(x) (sizeof(x)/sizeof(x[0]))
-void log_error(const char *fmt, ...);
+void log_error(const char *fmt, ...) __attribute__ ((format (printf, 1, 2)));
 #define fatal(...) { log_error(__VA_ARGS__); exit(EXIT_FAILURE); }
 
 typedef unsigned long long id_type;
diff --git a/kitty/fonts.c b/kitty/fonts.c
index 9f5cc2b9d..600475039 100644
--- a/kitty/fonts.c
+++ b/kitty/fonts.c
@@ -1105,7 +1105,7 @@ initialize_font(FontGroup *fg, unsigned int desc_idx, const char *ftype) {
     Py_CLEAR(face);
     if (!ok) {
         if (PyErr_Occurred()) { PyErr_Print(); }
-        fatal("Failed to initialize %s font: %d", ftype, idx);
+        fatal("Failed to initialize %s font: %zu", ftype, idx);
     }
     return idx;
 }