diff --git a/luna/include/luna/Format.h b/luna/include/luna/Format.h
index 28ffd1cd..6607e4d5 100644
--- a/luna/include/luna/Format.h
+++ b/luna/include/luna/Format.h
@@ -16,4 +16,4 @@ usize pure_cstyle_format(const char* format, pure_callback_t callback, void* arg
 usize vstring_format(char* buf, usize max, const char* format, va_list ap);
 
 // Convenience function which outputs into a fixed-size buffer (not unlike snprintf)
-usize string_format(char* buf, usize max, const char* format, ...);
\ No newline at end of file
+usize string_format(char* buf, usize max, const char* format, ...) _format(3, 4);
\ No newline at end of file
diff --git a/luna/src/Units.cpp b/luna/src/Units.cpp
index 85a73900..05afd720 100644
--- a/luna/src/Units.cpp
+++ b/luna/src/Units.cpp
@@ -6,7 +6,7 @@
 
 usize to_dynamic_unit_cstr(usize value, char* buffer, usize max)
 {
-    if (value < 1024) { return string_format(buffer, max, "%u bytes", value); }
+    if (value < 1024) { return string_format(buffer, max, "%zu bytes", value); }
 
     const char* unit_prefixes = "KMGTPE";
     while (value > (1024 * 1024))
@@ -15,7 +15,7 @@ usize to_dynamic_unit_cstr(usize value, char* buffer, usize max)
         unit_prefixes++;
     }
 
-    return string_format(buffer, max, "%u.%u %ciB", value / 1024, (value % 1024) / 103, *unit_prefixes);
+    return string_format(buffer, max, "%zu.%zu %ciB", value / 1024, (value % 1024) / 103, *unit_prefixes);
 }
 
 Result<OwnedStringView> to_dynamic_unit(usize value)