diff --git a/chacha.c b/chacha.c
index 541a7ac..ca52fe5 100644
--- a/chacha.c
+++ b/chacha.c
@@ -41,7 +41,7 @@ static const unsigned rounds = 8;
     a = PLUS(a, b); d = ROTATE(XOR(d, a), 8); \
     c = PLUS(c, d); b = ROTATE(XOR(b, c), 7);
 
-static const char sigma[16] = "expand 32-byte k";
+static const char sigma[16] NONSTRING = "expand 32-byte k";
 
 void chacha_keysetup(chacha_ctx *x, const u8 *k) {
     x->input[0] = U8TO32_LITTLE(sigma + 0);
diff --git a/util.h b/util.h
index 6b1a390..72c28d8 100644
--- a/util.h
+++ b/util.h
@@ -32,6 +32,13 @@
 #define STRINGIFY(s) #s
 #define ALIAS(f) __attribute__((alias(STRINGIFY(f))))
 
+// supported since GCC 15
+#if __has_attribute (nonstring)
+#  define NONSTRING __attribute__ ((nonstring))
+#else
+#  define NONSTRING
+#endif
+
 typedef uint8_t u8;
 typedef uint16_t u16;
 typedef uint32_t u32;