diff --git a/test/libsolidity/semanticTests/externalContracts/_stringutils/stringutils.sol b/test/libsolidity/semanticTests/externalContracts/_stringutils/stringutils.sol
index 47d8bd3f6..4dff7f916 100644
--- a/test/libsolidity/semanticTests/externalContracts/_stringutils/stringutils.sol
+++ b/test/libsolidity/semanticTests/externalContracts/_stringutils/stringutils.sol
@@ -52,8 +52,15 @@ library strings {
             src += 32;
         }
 
+        // The following masking would overflow in the case of len=0
+        // and the code path in that case is useless, albeit correct.
+        // This shortcut avoids it and saves gas.
+        if (len == 0)
+            return;
+
         // Copy remaining bytes
-        uint mask = 256 ** (32 - len) - 1;
+        uint mask;
+        unchecked { mask = 256 ** (32 - len) - 1; }
         assembly {
             let srcpart := and(mload(src), not(mask))
             let destpart := and(mload(dest), mask)
@@ -215,7 +222,9 @@ library strings {
                 if(shortest < 32) {
                   mask = ~(2 ** (8 * (32 - shortest + idx)) - 1);
                 }
-                uint256 diff = (a & mask) - (b & mask);
+                uint256 diff;
+                // This depends on potential underflow.
+                unchecked { diff = (a & mask) - (b & mask); }
                 if (diff != 0)
                     return int(diff);
             }
diff --git a/test/libsolidity/semanticTests/externalContracts/strings.sol b/test/libsolidity/semanticTests/externalContracts/strings.sol
index 6c16e205d..1f209ef6f 100644
--- a/test/libsolidity/semanticTests/externalContracts/strings.sol
+++ b/test/libsolidity/semanticTests/externalContracts/strings.sol
@@ -51,26 +51,26 @@ contract test {
 // compileViaYul: also
 // ----
 // constructor()
-// gas irOptimized: 926170
-// gas legacy: 1192776
-// gas legacyOptimized: 777238
+// gas irOptimized: 912777
+// gas legacy: 1188228
+// gas legacyOptimized: 771634
 // toSlice(string): 0x20, 11, "hello world" -> 11, 0xa0
 // gas irOptimized: 22877
 // gas legacy: 23190
 // gas legacyOptimized: 22508
 // roundtrip(string): 0x20, 11, "hello world" -> 0x20, 11, "hello world"
-// gas irOptimized: 23783
-// gas legacy: 24560
-// gas legacyOptimized: 23481
+// gas irOptimized: 23676
+// gas legacy: 23820
+// gas legacyOptimized: 23123
 // utf8len(string): 0x20, 16, "\xf0\x9f\x98\x83\xf0\x9f\x98\x83\xf0\x9f\x98\x83\xf0\x9f\x98\x83" -> 4 # Input: "😃😃😃😃" #
 // gas irOptimized: 24779
 // gas legacy: 25716
 // gas legacyOptimized: 24115
 // multiconcat(string,uint256): 0x40, 3, 11, "hello world" -> 0x20, 0x58, 0x68656c6c6f20776f726c6468656c6c6f20776f726c6468656c6c6f20776f726c, 0x6468656c6c6f20776f726c6468656c6c6f20776f726c6468656c6c6f20776f72, 49027192869463622675296414541903001712009715982962058146354235762728281047040 # concatenating 3 times #
-// gas irOptimized: 30478
-// gas legacy: 36801
-// gas legacyOptimized: 30420
-// benchmark(string,bytes32): 0x40, 0x0842021, 8, "solidity" -> FAILURE, hex"4e487b71", 0x11
-// gas irOptimized: 27298
+// gas irOptimized: 29729
 // gas legacy: 31621
-// gas legacyOptimized: 27668
+// gas legacyOptimized: 27914
+// benchmark(string,bytes32): 0x40, 0x0842021, 8, "solidity" -> 0x2020
+// gas irOptimized: 2903627
+// gas legacy: 4381235
+// gas legacyOptimized: 2317529