diff --git a/src/secp256k1/src/modules/schnorrsig/main_impl.h b/src/secp256k1/src/modules/schnorrsig/main_impl.h
index 9a08e81d8..00f241020 100644
--- a/src/secp256k1/src/modules/schnorrsig/main_impl.h
+++ b/src/secp256k1/src/modules/schnorrsig/main_impl.h
@@ -13,6 +13,7 @@
 
 static void secp256k1_scalar_chacha20(secp256k1_scalar *r1, secp256k1_scalar *r2, const unsigned char *seed, uint64_t idx);
 static int secp256k1_ecmult_multi_var(const secp256k1_ecmult_context *ctx, secp256k1_scratch *scratch, secp256k1_gej *r, const secp256k1_scalar *inp_g_sc, secp256k1_ecmult_multi_callback cb, void *cbdata, size_t n);
+typedef int (secp256k1_ecmult_multi_callback)(secp256k1_scalar *sc, secp256k1_ge *pt, size_t idx, void *data);
 
 int secp256k1_schnorrsig_serialize(const secp256k1_context* ctx, unsigned char *out64, const secp256k1_schnorrsig* sig) {
     (void) ctx;