diff --git a/include/fast_float/bigint.h b/include/fast_float/bigint.h
index 3fb1846..dc4db71 100644
--- a/include/fast_float/bigint.h
+++ b/include/fast_float/bigint.h
@@ -39,7 +39,7 @@ constexpr limb_t bigint_limbs = bigint_bits / limb_bits;
 // vector-like type that is allocated on the stack. the entire
 // buffer is pre-allocated, and only the length changes.
 template <limb_t size> struct stackvec {
-  limb data[size];
+  limb data[size] = {0};
   // we never need more than 150 limbs
   uint_fast8_t length{0};