diff --git a/thirdparty/README.md b/thirdparty/README.md
index ac1ce6d5fc0..f590acaa0b2 100644
--- a/thirdparty/README.md
+++ b/thirdparty/README.md
@@ -378,7 +378,7 @@ Collection of single-file libraries used in Godot components.
   * License: Apache 2.0
 - `open-simplex-noise.{c,h}`
   * Upstream: https://github.com/smcameron/open-simplex-noise-in-c
-  * Version: git (0d555e7f40527d0870906fe9469a3b1bb4020b7f, 2015) + custom changes
+  * Version: git (0fef0dbedd76f767da7e3c894822729d0f07e54d, 2020) + custom changes
   * License: Unlicense
 - `pcg.{cpp,h}`
   * Upstream: http://www.pcg-random.org
diff --git a/thirdparty/misc/open-simplex-noise.c b/thirdparty/misc/open-simplex-noise.c
index 42f2fbb5bed..88fbd3e51d7 100644
--- a/thirdparty/misc/open-simplex-noise.c
+++ b/thirdparty/misc/open-simplex-noise.c
@@ -189,14 +189,15 @@ int open_simplex_noise(int64_t seed, struct osn_context *ctx)
 	permGradIndex3D = ctx->permGradIndex3D;
 // -- GODOT end --
 
+	uint64_t seedU = seed;
 	for (i = 0; i < 256; i++)
 		source[i] = (int16_t) i;
-	seed = seed * 6364136223846793005LL + 1442695040888963407LL;
-	seed = seed * 6364136223846793005LL + 1442695040888963407LL;
-	seed = seed * 6364136223846793005LL + 1442695040888963407LL;
+	seedU = seedU * 6364136223846793005ULL + 1442695040888963407ULL;
+	seedU = seedU * 6364136223846793005ULL + 1442695040888963407ULL;
+	seedU = seedU * 6364136223846793005ULL + 1442695040888963407ULL;
 	for (i = 255; i >= 0; i--) {
-		seed = seed * 6364136223846793005LL + 1442695040888963407LL;
-		r = (int)((seed + 31) % (i + 1));
+		seedU = seedU * 6364136223846793005ULL + 1442695040888963407ULL;
+		r = (int)((seedU + 31) % (i + 1));
 		if (r < 0)
 			r += (i + 1);
 		perm[i] = source[r];