diff --git a/lib/ngtcp2_cc.c b/lib/ngtcp2_cc.c
index 3a0a7d8afc66971160ca86f901621090cbf6b021..384916b7168f8b1a32b4498221c6b763eb2c907d 100644
--- a/lib/ngtcp2_cc.c
+++ b/lib/ngtcp2_cc.c
@@ -24,7 +24,6 @@
  */
 #include "ngtcp2_cc.h"
 
-#include <assert.h>
 
 #include "ngtcp2_log.h"
 #include "ngtcp2_macro.h"
diff --git a/lib/ngtcp2_gaptr.c b/lib/ngtcp2_gaptr.c
index cdbecd1df1e45fe991608334ae0b71757d1d360c..b4b6ce06dc986897460c19ec1803add941902d1b 100644
--- a/lib/ngtcp2_gaptr.c
+++ b/lib/ngtcp2_gaptr.c
@@ -25,7 +25,6 @@
 #include "ngtcp2_gaptr.h"
 
 #include <string.h>
-#include <assert.h>
 
 #include "ngtcp2_macro.h"
 
diff --git a/lib/ngtcp2_str.c b/lib/ngtcp2_str.c
index 4223a0ffdff01d62e86e0f989e7ba9f692a36d79..4d0b9b413137123f89ccd90988648c0ede666545 100644
--- a/lib/ngtcp2_str.c
+++ b/lib/ngtcp2_str.c
@@ -25,7 +25,6 @@
 #include "ngtcp2_str.h"
 
 #include <string.h>
-#include <assert.h>
 
 void *ngtcp2_cpymem(void *dest, const void *src, size_t n) {
   memcpy(dest, src, n);
diff --git a/tests/ngtcp2_conv_test.c b/tests/ngtcp2_conv_test.c
index 80b8d75ffa3fe045c83164d63a569de9e4d4be0e..c8094fcf43153d0767abc41706122870ef65c0b0 100644
--- a/tests/ngtcp2_conv_test.c
+++ b/tests/ngtcp2_conv_test.c
@@ -24,7 +24,6 @@
  */
 #include "ngtcp2_conv_test.h"
 
-#include <assert.h>
 
 #include <CUnit/CUnit.h>
 
diff --git a/tests/ngtcp2_crypto_test.c b/tests/ngtcp2_crypto_test.c
index 2ea41885e79b7c452be26ef9705910c9265cd064..4acb6ea9314402f0179fc8507989719e8a1d622c 100644
--- a/tests/ngtcp2_crypto_test.c
+++ b/tests/ngtcp2_crypto_test.c
@@ -24,7 +24,6 @@
  */
 #include "ngtcp2_crypto_test.h"
 
-#include <assert.h>
 
 #include <CUnit/CUnit.h>
 
diff --git a/tests/ngtcp2_pkt_test.c b/tests/ngtcp2_pkt_test.c
index 3da67b4967e9219d10b9724c92d68241f34e883d..6be4a647e424c4119652506af8010f6e12915c19 100644
--- a/tests/ngtcp2_pkt_test.c
+++ b/tests/ngtcp2_pkt_test.c
@@ -24,7 +24,6 @@
  */
 #include "ngtcp2_pkt_test.h"
 
-#include <assert.h>
 
 #include <CUnit/CUnit.h>