diff --git a/src/ops.rs b/src/ops.rs
index 8431556..6f8780a 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -9,7 +9,15 @@ impl Neg for SmallInt {
 
     fn neg(self) -> Self::Output {
         match self.0 {
-            SmallIntType::Inline(i) => SmallInt(SmallIntType::Inline(-i)),
+            SmallIntType::Inline(i) => {
+                if let Some(n) = i.checked_neg() {
+                    SmallInt(SmallIntType::Inline(n))
+                } else {
+                    // -i128::MIN = i128::MAX + 1 = 0x8000...
+                    let mut val = ManuallyDrop::new(Box::new([0, 0, 0, 0x80_00_00_00]));
+                    SmallInt(SmallIntType::Heap((val.as_mut_ptr(), 4)))
+                }
+            },
             SmallIntType::Heap((r, s)) => {
                 let size = usize::try_from(s.abs()).unwrap();
                 let slice = unsafe { core::slice::from_raw_parts(r, size) };
diff --git a/src/tests.rs b/src/tests.rs
index a8a3c8e..f7d3666 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -320,9 +320,13 @@ fn test_op_neg() {
     let q = -i;
     assert_eq!(BigInt::from(&q), -BigInt::from(u128::MAX));
 
-    let i = SmallInt::from(i64::MIN);
+    let i = SmallInt::from(i128::MAX);
     let q = -i;
-    assert_eq!(BigInt::from(&q), -BigInt::from(i64::MIN));
+    assert_eq!(BigInt::from(&q), -BigInt::from(i128::MAX));
+
+    let i = SmallInt::from(i128::MIN);
+    let q = -i;
+    assert_eq!(BigInt::from(&q), -BigInt::from(i128::MIN));
 }
 
 #[test]