diff --git a/mrbgems/mruby-devmem/src/devmem.c b/mrbgems/mruby-devmem/src/devmem.c
index a9dc3e0..b21107e 100644
--- a/mrbgems/mruby-devmem/src/devmem.c
+++ b/mrbgems/mruby-devmem/src/devmem.c
@@ -36,11 +36,11 @@ static mrb_value mrb_read8(mrb_state *mrb, mrb_value self) {
 }
 
 static mrb_value mrb_write32(mrb_state *mrb, mrb_value self) {
-    mrb_value addr, value;
-    mrb_get_args(mrb, "i|i", &addr, &value);
+    mrb_int addr, value;
+    mrb_get_args(mrb, "ii", &addr, &value);
 
-    uint32_t addr_int  = mrb_integer(addr);
-    uint32_t value_int = mrb_integer(value);
+    uint32_t addr_int  = (uint32_t)addr;
+    uint32_t value_int = (uint32_t)value;
 
     if (addr_int % 4 != 0) {
         mrb_raise(mrb, E_ARGUMENT_ERROR, "Address must be 32bits aligned");
@@ -48,15 +48,15 @@ static mrb_value mrb_write32(mrb_state *mrb, mrb_value self) {
 
     *(volatile uint16_t *)(addr_int) = value_int;
 
-    return self;
+    return mrb_nil_value();
 }
 
 static mrb_value mrb_write16(mrb_state *mrb, mrb_value self) {
-    mrb_value addr, value;
-    mrb_get_args(mrb, "i|i", &addr, &value);
+    mrb_int addr, value;
+    mrb_get_args(mrb, "ii", &addr, &value);
 
-    uint32_t addr_int  = mrb_integer(addr);
-    uint16_t value_int = mrb_integer(value);
+    uint32_t addr_int  = (uint32_t)addr;
+    uint16_t value_int = (uint16_t)value;
 
     if (addr_int % 2 != 0) {
         mrb_raise(mrb, E_ARGUMENT_ERROR, "Address must be 16bits aligned");
@@ -64,19 +64,19 @@ static mrb_value mrb_write16(mrb_state *mrb, mrb_value self) {
 
     *(volatile uint16_t *)(addr_int) = value_int;
 
-    return self;
+    return mrb_nil_value();
 }
 
 static mrb_value mrb_write8(mrb_state *mrb, mrb_value self) {
-    mrb_value addr, value;
-    mrb_get_args(mrb, "i|i", &addr, &value);
+    mrb_int addr, value;
+    mrb_get_args(mrb, "ii", &addr, &value);
 
-    uint32_t addr_int  = mrb_integer(addr);
-    uint16_t value_int = mrb_integer(value);
+    uint32_t addr_int  = (uint32_t)addr;
+    uint8_t value_int = (uint8_t)value;
 
     *(volatile uint8_t *)(addr_int) = value_int;
 
-    return self;
+    return mrb_nil_value();
 }
 
 void mrb_mruby_devmem_gem_init(mrb_state *mrb) {