diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index 8fd02e49cded..a44561fb1e69 100644
--- a/lib/tests/misc.nix
+++ b/lib/tests/misc.nix
@@ -380,8 +380,9 @@ runTests {
     expected = 255;
   };
 
-  testFromHexStringSecondExample = {
-    expr = fromHexString (builtins.hashString "sha256" "test");
+  # Highest supported integer value in Nix.
+  testFromHexStringMaximum = {
+    expr = fromHexString "7fffffffffffffff";
     expected = 9223372036854775807;
   };
 
diff --git a/lib/trivial.nix b/lib/trivial.nix
index eba6dd69b12e..ada83b8fb4be 100644
--- a/lib/trivial.nix
+++ b/lib/trivial.nix
@@ -1114,7 +1114,7 @@ in
     fromHexString "FF"
     => 255
 
-    fromHexString (builtins.hashString "sha256" "test")
+    fromHexString "0x7fffffffffffffff"
     => 9223372036854775807
     ```
   */