diff --git a/include/mruby/istruct.h b/include/mruby/istruct.h
index 4d2393ccd..23c9bfa36 100644
--- a/include/mruby/istruct.h
+++ b/include/mruby/istruct.h
@@ -19,12 +19,12 @@ MRB_BEGIN_DECL
 
 #define ISTRUCT_DATA_SIZE (sizeof(void*) * 3)
 
-struct RIstruct {
+struct RIStruct {
   MRB_OBJECT_HEADER;
   char inline_data[ISTRUCT_DATA_SIZE];
 };
 
-#define RISTRUCT(obj)         ((struct RIstruct*)(mrb_ptr(obj)))
+#define RISTRUCT(obj)         ((struct RIStruct*)(mrb_ptr(obj)))
 #define ISTRUCT_PTR(obj)      (RISTRUCT(obj)->inline_data)
 
 MRB_INLINE mrb_int mrb_istruct_size()
diff --git a/src/gc.c b/src/gc.c
index 5e7440d50..6dc8e373b 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -110,7 +110,7 @@ typedef struct {
     struct RHash hash;
     struct RRange range;
     struct RData data;
-    struct RIstruct istruct;
+    struct RIStruct istruct;
     struct RProc proc;
     struct REnv env;
     struct RFiber fiber;