diff --git a/src/mem/sizeclass.h b/src/mem/sizeclass.h
index e5bb6e3f9..801192d83 100644
--- a/src/mem/sizeclass.h
+++ b/src/mem/sizeclass.h
@@ -188,10 +188,14 @@ namespace snmalloc
 
   SNMALLOC_FAST_PATH static size_t round_size(size_t size)
   {
-    if (size > size_to_sizeclass(NUM_SIZECLASSES - 1))
+    if (size > sizeclass_to_size(NUM_SIZECLASSES - 1))
     {
       return bits::next_pow2(size);
     }
+    if (size == 0)
+    {
+      size = 1;
+    }
     return sizeclass_to_size(size_to_sizeclass(size));
   }
 } // namespace snmalloc
diff --git a/src/test/func/malloc/malloc.cc b/src/test/func/malloc/malloc.cc
index d648d9593..029428d74 100644
--- a/src/test/func/malloc/malloc.cc
+++ b/src/test/func/malloc/malloc.cc
@@ -15,22 +15,39 @@ void check_result(size_t size, size_t align, void* p, int err, bool null)
   {
     if (p != nullptr)
       abort();
-  }
-  else
-  {
-    auto asize = our_malloc_usable_size(p);
-    if (asize < size)
-    {
-      printf(
-        "Usable size is %zu, but required to be at least %zu.\n", asize, size);
-      abort();
-    }
-
-    if (static_cast<size_t>(reinterpret_cast<uintptr_t>(p) % align) != 0)
-      abort();
 
     our_free(p);
+    return;
+  }
+
+  const auto alloc_size = our_malloc_usable_size(p);
+  const auto expected_size = round_size(size);
+  if ((align == 1) && (alloc_size != expected_size))
+  {
+    printf(
+      "Usable size is %zu, but required to be %zu.\n",
+      alloc_size,
+      expected_size);
+    abort();
+  }
+  if ((align != 1) && (alloc_size < expected_size))
+  {
+    printf(
+      "Usable size is %zu, but required to be at least %zu.\n",
+      alloc_size,
+      expected_size);
+    abort();
   }
+  if (static_cast<size_t>(reinterpret_cast<uintptr_t>(p) % align) != 0)
+  {
+    printf(
+      "Address is 0x%zx, but required to be aligned to 0x%zx.\n",
+      reinterpret_cast<uintptr_t>(p),
+      align);
+    abort();
+  }
+
+  our_free(p);
 }
 
 void test_calloc(size_t nmemb, size_t size, int err, bool null)
@@ -92,7 +109,7 @@ int main(int argc, char** argv)
 
   test_realloc(our_malloc(64), 4194304, SUCCESS, false);
 
-  for (snmalloc::sizeclass_t sc = 0; sc < (SUPERSLAB_BITS + 4); sc++)
+  for (sizeclass_t sc = 0; sc < (SUPERSLAB_BITS + 4); sc++)
   {
     const size_t size = 1ULL << sc;
     printf("malloc: %zu\n", size);
@@ -102,7 +119,7 @@ int main(int argc, char** argv)
 
   test_calloc(0, 0, SUCCESS, false);
 
-  for (snmalloc::sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
+  for (sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
   {
     const size_t size = sizeclass_to_size(sc);
 
@@ -118,14 +135,14 @@ int main(int argc, char** argv)
     test_calloc(0, size, SUCCESS, false);
   }
 
-  for (snmalloc::sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
+  for (sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
   {
     const size_t size = sizeclass_to_size(sc);
     test_realloc(our_malloc(size), size, SUCCESS, false);
     test_realloc(our_malloc(size), 0, SUCCESS, true);
     test_realloc(nullptr, size, SUCCESS, false);
     test_realloc(our_malloc(size), (size_t)-1, ENOMEM, true);
-    for (snmalloc::sizeclass_t sc2 = 0; sc2 < NUM_SIZECLASSES; sc2++)
+    for (sizeclass_t sc2 = 0; sc2 < NUM_SIZECLASSES; sc2++)
     {
       const size_t size2 = sizeclass_to_size(sc2);
       test_realloc(our_malloc(size), size2, SUCCESS, false);
@@ -133,14 +150,14 @@ int main(int argc, char** argv)
     }
   }
 
-  for (snmalloc::sizeclass_t sc = 0; sc < (SUPERSLAB_BITS + 4); sc++)
+  for (sizeclass_t sc = 0; sc < (SUPERSLAB_BITS + 4); sc++)
   {
     const size_t size = 1ULL << sc;
     test_realloc(our_malloc(size), size, SUCCESS, false);
     test_realloc(our_malloc(size), 0, SUCCESS, true);
     test_realloc(nullptr, size, SUCCESS, false);
     test_realloc(our_malloc(size), (size_t)-1, ENOMEM, true);
-    for (snmalloc::sizeclass_t sc2 = 0; sc2 < (SUPERSLAB_BITS + 4); sc2++)
+    for (sizeclass_t sc2 = 0; sc2 < (SUPERSLAB_BITS + 4); sc2++)
     {
       const size_t size2 = 1ULL << sc2;
       printf("size1: %zu, size2:%zu\n", size, size2);
@@ -156,7 +173,7 @@ int main(int argc, char** argv)
   for (size_t align = sizeof(uintptr_t); align <= SUPERSLAB_SIZE * 8;
        align <<= 1)
   {
-    for (snmalloc::sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
+    for (sizeclass_t sc = 0; sc < NUM_SIZECLASSES; sc++)
     {
       const size_t size = sizeclass_to_size(sc);
       test_posix_memalign(size, align, SUCCESS, false);