diff --git a/include/picrin.h b/include/picrin.h
index 8ac8bc21..db4b823d 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -32,6 +32,7 @@ extern "C" {
 #include <stdbool.h>
 #include <setjmp.h>
 #include <stdio.h>
+#include <assert.h>
 
 #include "xhash/xhash.h"
 #include "xfile/xfile.h"
diff --git a/src/codegen.c b/src/codegen.c
index 66cff6fb..7bfa7805 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -2,9 +2,6 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
-#include <assert.h>
-
 #include "picrin.h"
 #include "picrin/pair.h"
 #include "picrin/irep.h"
diff --git a/src/error.c b/src/error.c
index cb1ba861..5e6fee08 100644
--- a/src/error.c
+++ b/src/error.c
@@ -3,7 +3,6 @@
  */
 
 #include <stdlib.h>
-#include <stdio.h>
 #include <string.h>
 #include <stdarg.h>
 
diff --git a/src/file.c b/src/file.c
index bb46b9f0..50f7a646 100644
--- a/src/file.c
+++ b/src/file.c
@@ -2,8 +2,6 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
-
 #include "picrin.h"
 #include "picrin/port.h"
 
diff --git a/src/gc.c b/src/gc.c
index 9e1734ff..62cbd76d 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -18,8 +18,6 @@
 
 #if GC_DEBUG
 # include <string.h>
-# include <stdio.h>
-# include <assert.h>
 #endif
 
 void
diff --git a/src/init.c b/src/init.c
index 8b5abdac..be998436 100644
--- a/src/init.c
+++ b/src/init.c
@@ -2,7 +2,6 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
 #include <stdlib.h>
 
 #include "picrin.h"
diff --git a/src/macro.c b/src/macro.c
index 278bade7..a631cc16 100644
--- a/src/macro.c
+++ b/src/macro.c
@@ -2,8 +2,6 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
-#include <assert.h>
 #include <string.h>
 
 #include "picrin.h"
diff --git a/src/parse.y b/src/parse.y
index 411e6077..6072acf1 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -4,7 +4,6 @@
 
 %{
 #include <stdlib.h>
-#include <stdio.h>
 #include <string.h>
 
 #include "picrin.h"
diff --git a/src/port.c b/src/port.c
index 93a422a4..27eb0c3a 100644
--- a/src/port.c
+++ b/src/port.c
@@ -2,10 +2,8 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <assert.h>
 
 #include "picrin.h"
 #include "picrin/proc.h"
diff --git a/src/symbol.c b/src/symbol.c
index 8cd1f62c..507746e4 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -5,7 +5,6 @@
 #include <string.h>
 #include <stdlib.h>
 #include <math.h>
-#include <assert.h>
 
 #include "picrin.h"
 
diff --git a/src/var.c b/src/var.c
index a9aa653b..9219ddb4 100644
--- a/src/var.c
+++ b/src/var.c
@@ -6,8 +6,6 @@
 #include "picrin/proc.h"
 #include "picrin/var.h"
 
-#include <assert.h>
-
 #define UNREACHABLE (assert(false))
 
 struct pic_var *
diff --git a/src/vm.c b/src/vm.c
index 6c524ce8..fe5fb3e9 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -2,7 +2,6 @@
  * See Copyright Notice in picrin.h
  */
 
-#include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
 #include <limits.h>