diff --git a/libc/src/stdio/printf_core/core_structs.h b/libc/src/stdio/printf_core/core_structs.h
index e96bc4dc0f8dd3..88a13703fd9476 100644
--- a/libc/src/stdio/printf_core/core_structs.h
+++ b/libc/src/stdio/printf_core/core_structs.h
@@ -53,7 +53,7 @@ struct FormatSection {
 
   // This operator is only used for testing and should be automatically
   // optimized out for release builds.
-  bool operator==(const FormatSection &other) {
+  bool operator==(const FormatSection &other) const {
     if (has_conv != other.has_conv)
       return false;