diff --git a/util/crossgcc/buildgcc b/util/crossgcc/buildgcc
index 1b0c89ae1c..57aeb96ab5 100755
--- a/util/crossgcc/buildgcc
+++ b/util/crossgcc/buildgcc
@@ -654,7 +654,9 @@ build_GMP() {
 	fi
 
 	# shellcheck disable=SC2086
-	CC="$(hostcc host)" CXX="$(hostcxx host)" \
+	# Bug: GMP currently does not support being build by GCC 15 (--std=gnu23)
+	#      Remove CFLAGS once it works again.
+	CC="$(hostcc host)" CXX="$(hostcxx host)" CFLAGS="-std=gnu17" \
 	../${GMP_DIR}/configure \
 		--disable-shared \
 		--enable-fat \