diff --git a/src/parser.c b/src/parser.c
index 1110582..5a46b25 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -79,9 +79,11 @@ static enum parse_fragment_result parse_fragment(apfl_parser_ptr, struct fragmen
 static bool
 grow_fragment_cap(struct fragment_list *list, size_t inc)
 {
-    return apfl_resizable_grow_cap(
+    return apfl_resizable_ensure_cap_for_more_elements(
         sizeof(struct fragment),
-        APFL_RESIZABLE_ARGS(*list, children),
+        (void **)&list->children,
+        list->len,
+        &list->cap,
         inc
     );
 }
@@ -1536,9 +1538,11 @@ break_inner:
                 goto error;
             }
 
-            if (!apfl_resizable_grow_cap(
+            if (!apfl_resizable_ensure_cap_for_more_elements(
                 sizeof(struct partial_assignment),
-                APFL_RESIZABLE_ARGS(partial_assignments, items),
+                (void **)&partial_assignments.items,
+                partial_assignments.len,
+                &partial_assignments.cap,
                 1
             )) {
                 p->error = apfl_error_simple(APFL_ERR_MALLOC_FAILED);
diff --git a/src/resizable.c b/src/resizable.c
index 895f80a..9e00733 100644
--- a/src/resizable.c
+++ b/src/resizable.c
@@ -25,7 +25,7 @@ apfl_resizable_resize(size_t elem_size, void **mem, size_t *len, size_t *cap, si
 
     assert(newlen >= *cap);
 
-    if (!apfl_resizable_grow_cap(elem_size, mem, len, cap, newlen - *cap)) {
+    if (!apfl_resizable_ensure_cap(elem_size, mem, cap, newlen)) {
         return false;
     }
 
@@ -34,37 +34,36 @@ apfl_resizable_resize(size_t elem_size, void **mem, size_t *len, size_t *cap, si
 }
 
 bool
-apfl_resizable_grow_cap(size_t elem_size, void **mem, size_t *len, size_t *cap, size_t inc_cap)
+apfl_resizable_ensure_cap(size_t elem_size, void **mem, size_t *cap, size_t want_cap)
 {
-    (void)len;// \mystuff\TODO:better not even have the arg
-
-    if (inc_cap == 0) {
+    if (want_cap <= *cap) {
         return true;
     }
 
-    size_t newcap = *cap + inc_cap;
-
     // TODO: We currently simply grow the memory to have space for exactly
-    //       inc_cap more elements. It would probably be smarter to grow the
-    //       memory a bit larger to reduce calls to realloc.
-    void *newmem = realloc(*mem, newcap * elem_size);
+    //       want_cap elements. It would probably be smarter to grow the memory
+    //       a bit larger to reduce calls to realloc.
+    void *newmem = realloc(*mem, want_cap * elem_size);
     if (newmem == NULL) {
         return false;
     }
 
     *mem = newmem;
-    *cap = newcap;
+    *cap = want_cap;
     return true;
 }
 
+bool
+apfl_resizable_ensure_cap_for_more_elements(size_t elem_size, void **mem, size_t len, size_t *cap, size_t more_elements)
+{
+    return apfl_resizable_ensure_cap(elem_size, mem, cap, len + more_elements); // TODO: What if len + more_elements overflows?
+}
+
 bool
 apfl_resizable_append(size_t elem_size, void **mem, size_t *len, size_t *cap, const void *other_mem, size_t other_len)
 {
-    size_t newlen = *len + other_len;
-    if (newlen > *cap) {
-        if (!apfl_resizable_grow_cap(elem_size, mem, len, cap, newlen - *cap)) {
-            return false;
-        }
+    if (!apfl_resizable_ensure_cap_for_more_elements(elem_size, mem, *len, cap, other_len)) {
+        return false;
     }
 
     memcpy(*((char**)mem) + (elem_size * *len), other_mem, other_len * elem_size);
diff --git a/src/resizable.h b/src/resizable.h
index 806862e..fe7d12c 100644
--- a/src/resizable.h
+++ b/src/resizable.h
@@ -15,7 +15,9 @@ void apfl_resizable_init(void **mem, size_t *len, size_t *cap);
 
 bool apfl_resizable_resize(size_t elem_size, void **mem, size_t *len, size_t *cap, size_t newlen);
 
-bool apfl_resizable_grow_cap(size_t elem_size, void **mem, size_t *len, size_t *cap, size_t inc_cap);
+bool apfl_resizable_ensure_cap(size_t elem_size, void **mem, size_t *cap, size_t want_cap);
+bool apfl_resizable_ensure_cap_for_more_elements(size_t elem_size, void **mem, size_t len, size_t *cap, size_t more_elements);
+
 
 bool apfl_resizable_append(size_t elem_size, void **mem, size_t *len, size_t *cap, const void *other_mem, size_t other_len);