diff --git a/core/iwasm/common/wasm_c_api.c b/core/iwasm/common/wasm_c_api.c
index 0019b5eee..04ec4e383 100644
--- a/core/iwasm/common/wasm_c_api.c
+++ b/core/iwasm/common/wasm_c_api.c
@@ -392,8 +392,8 @@ wasm_engine_new_internal(wasm_config_t *config)
 
     WASM_C_DUMP_PROC_MEM();
 
-    /* wasm_config_t->MemAllocOption -> RuntimeInitArgs->MemAllocOption */
     init_args.gc_heap_size = GC_HEAP_SIZE_DEFAULT;
+    /* wasm_config_t->MemAllocOption -> RuntimeInitArgs->MemAllocOption */
     init_args.mem_alloc_type = config->mem_alloc_type;
     memcpy(&init_args.mem_alloc_option, &config->mem_alloc_option,
            sizeof(MemAllocOption));
diff --git a/doc/build_wamr.md b/doc/build_wamr.md
index cde884457..64be528bd 100644
--- a/doc/build_wamr.md
+++ b/doc/build_wamr.md
@@ -141,6 +141,7 @@ cmake -DWAMR_BUILD_PLATFORM=linux -DWAMR_BUILD_TARGET=ARM
 
 ### **Enable Garbage Collection**
 - **WAMR_BUILD_GC**=1/0, default to disable if not set
+- **WAMR_BUILD_GC_HEAP_SIZE_DEFAULT**=n, default to 128 kB (131072) if not set
 
 ### **Configure Debug**