diff --git a/eclass/toolchain.eclass b/eclass/toolchain.eclass
index 01fbd62dc12c1..6a515f9b5c690 100644
--- a/eclass/toolchain.eclass
+++ b/eclass/toolchain.eclass
@@ -1619,9 +1619,16 @@ gcc_do_filter_flags() {
 			[[ -n ${l1_cache_size} && ${l1_cache_size} =~ ^[0-9]+$ ]] || break
 			l1_cache_sizes[${l1_cache_size}]=1
 		done
-		# If any of them are different, just pick the first one.
+		# If any of them are different, abort. We can't just pass one value of
+		# l1-cache-size because it doesn't cancel out the -march=native one.
 		if [[ ${#l1_cache_sizes[@]} -gt 1 ]] ; then
-			append-flags --param=l1-cache-size=${l1_cache_size}
+			eerror "Different values of l1-cache-size detected!"
+			eerror "GCC will fail to bootstrap when comparing files with these flags."
+			eerror "This CPU is likely big.little/hybrid hardware with power/efficiency cores."
+			eerror "Please install app-misc/resolve-march-native and run 'resolve-march-native'"
+			eerror "to find a safe value of CFLAGS for this CPU. Note that this may vary"
+			eerror "depending on the core it ran on. taskset can be used to fix the cores used."
+			die "Varying l1-cache-size found, aborting (bug #915389, gcc PR#111768)"
 		fi
 	fi