diff --git a/ext/digest/blake3/extconf.rb b/ext/digest/blake3/extconf.rb
index df844d0..93e88fa 100644
--- a/ext/digest/blake3/extconf.rb
+++ b/ext/digest/blake3/extconf.rb
@@ -78,6 +78,15 @@ def blake3_have_isa?(name, flag, snippet)
 
 have_header("sys/cdefs.h")
 
+checking_for("C11 atomics") do
+  unless try_compile(<<~C)
+      static _Atomic int atomic_int = 0;
+      int main(void){ return 0 }
+    C
+    $defs << "-DBLAKE3_ATOMICS=0"
+  end
+end
+
 $preload = %w[digest]
 
 create_makefile("digest/blake3")