diff --git a/src/hsort_impl.h b/src/hsort_impl.h
index a6ff32ab35..24fc59add6 100644
--- a/src/hsort_impl.h
+++ b/src/hsort_impl.h
@@ -23,20 +23,22 @@ static SECP256K1_INLINE size_t secp256k1_heap_child2(size_t i) {
     return secp256k1_heap_child1(i)+1;
 }
 
-static SECP256K1_INLINE void secp256k1_heap_swap64(unsigned char *a, size_t i, size_t j, size_t stride) {
+static SECP256K1_INLINE void secp256k1_heap_swap64(unsigned char *a, size_t i, size_t j, size_t stride, size_t swap_size) {
     unsigned char tmp[64];
-    VERIFY_CHECK(stride <= 64);
-    memcpy(tmp, a + i*stride, stride);
-    memmove(a + i*stride, a + j*stride, stride);
-    memcpy(a + j*stride, tmp, stride);
+    VERIFY_CHECK(swap_size <= 64);
+    memcpy(tmp, a + i*stride, swap_size);
+    memmove(a + i*stride, a + j*stride, swap_size);
+    memcpy(a + j*stride, tmp, swap_size);
 }
 
+/* Swap the elements of a at indices i and j, assuming that the size of each element is stride. */
 static SECP256K1_INLINE void secp256k1_heap_swap(unsigned char *a, size_t i, size_t j, size_t stride) {
-    while (64 < stride) {
-        secp256k1_heap_swap64(a + (stride - 64), i, j, 64);
-        stride -= 64;
+    size_t remaining = stride;
+    while (64 < remaining) {
+        secp256k1_heap_swap64(a + (remaining - 64), i, j, stride, 64);
+        remaining -= 64;
     }
-    secp256k1_heap_swap64(a, i, j, stride);
+    secp256k1_heap_swap64(a, i, j, stride, remaining);
 }
 
 static SECP256K1_INLINE void secp256k1_heap_down(unsigned char *a, size_t i, size_t heap_size, size_t stride,
diff --git a/src/tests.c b/src/tests.c
index 4d3f22e16a..39407b0a20 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -6607,6 +6607,18 @@ static void run_pubkey_comparison(void) {
     CHECK(secp256k1_ec_pubkey_cmp(CTX, &pk2, &pk1) > 0);
 }
 
+static void test_heap_swap(void) {
+    unsigned char a[600];
+    unsigned char e[sizeof(a)];
+    memset(a,       21, 200);
+    memset(a + 200, 99, 200);
+    memset(a + 400, 42, 200);
+    memset(e,       42, 200);
+    memset(e + 200, 99, 200);
+    memset(e + 400, 21, 200);
+    secp256k1_heap_swap(a, 0, 2, 200);
+    CHECK(secp256k1_memcmp_var(a, e, sizeof(a)) == 0);
+}
 
 static void test_hsort_is_sorted(int *ints, size_t n) {
     size_t i;
@@ -6801,6 +6813,7 @@ static void run_pubkey_sort(void) {
     test_sort_api();
     test_sort();
     test_sort_vectors();
+    test_heap_swap();
 }