diff --git a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
index 957bd732fed57..5ce7919e830bf 100644
--- a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
+++ b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
@@ -467,8 +467,8 @@ private static bool HexNumberToBigInteger(ref BigNumberBuffer number, out BigInt
 
                     if ((!isNegative && sign < 0) || sign == int.MinValue)
                     {
-                        sign = isNegative ? -1 : 1;
                         bits = new[] { (uint)sign };
+                        sign = isNegative ? -1 : 1;
                     }
                 }
                 else
diff --git a/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs b/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
index 23440b41d95e3..115a61366d093 100644
--- a/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
+++ b/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
@@ -105,6 +105,19 @@ public void Parse_EmptySubspan_Fails()
             Assert.Equal(0, result);
         }
 
+        [Fact]
+        public void Parse_Hex32Bits()
+        {
+            // Regression test for: https://github.com/dotnet/runtime/issues/54251
+            BigInteger result;
+
+            Assert.True(BigInteger.TryParse("80000000", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(int.MinValue, result);
+
+            Assert.True(BigInteger.TryParse("080000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(0x80000001u, result);
+        }
+
         private static void RunFormatProviderParseStrings()
         {
             NumberFormatInfo nfi = new NumberFormatInfo();