diff --git a/ChangeLog.d/bugfix_3782.txt b/ChangeLog.d/bugfix_3782.txt
new file mode 100644
index 000000000..25e18cb18
--- /dev/null
+++ b/ChangeLog.d/bugfix_3782.txt
@@ -0,0 +1,2 @@
+Bugfix
+  * Fix build failures on GCC 11. Fixes #3782.
diff --git a/library/cmac.c b/library/cmac.c
index 1a1200b52..409f67958 100644
--- a/library/cmac.c
+++ b/library/cmac.c
@@ -450,7 +450,7 @@ exit:
  */
 int mbedtls_aes_cmac_prf_128( const unsigned char *key, size_t key_length,
                               const unsigned char *input, size_t in_len,
-                              unsigned char *output )
+                              unsigned char output[16] )
 {
     int ret;
     const mbedtls_cipher_info_t *cipher_info;
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 2471600c9..c749a8611 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -621,7 +621,7 @@ static void ssl_calc_finished_tls( mbedtls_ssl_context *, unsigned char *, int )
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 #if defined(MBEDTLS_SHA256_C)
 static void ssl_update_checksum_sha256( mbedtls_ssl_context *, const unsigned char *, size_t );
-static void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *,unsigned char * );
+static void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *, unsigned char * );
 static void ssl_calc_finished_tls_sha256( mbedtls_ssl_context *,unsigned char *, int );
 #endif
 
@@ -1142,7 +1142,7 @@ int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl )
 }
 
 #if defined(MBEDTLS_SSL_PROTO_SSL3)
-void ssl_calc_verify_ssl( mbedtls_ssl_context *ssl, unsigned char hash[36] )
+void ssl_calc_verify_ssl( mbedtls_ssl_context *ssl, unsigned char *hash )
 {
     mbedtls_md5_context md5;
     mbedtls_sha1_context sha1;
@@ -1191,7 +1191,7 @@ void ssl_calc_verify_ssl( mbedtls_ssl_context *ssl, unsigned char hash[36] )
 #endif /* MBEDTLS_SSL_PROTO_SSL3 */
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
-void ssl_calc_verify_tls( mbedtls_ssl_context *ssl, unsigned char hash[36] )
+void ssl_calc_verify_tls( mbedtls_ssl_context *ssl, unsigned char *hash )
 {
     mbedtls_md5_context md5;
     mbedtls_sha1_context sha1;
@@ -1219,7 +1219,7 @@ void ssl_calc_verify_tls( mbedtls_ssl_context *ssl, unsigned char hash[36] )
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 #if defined(MBEDTLS_SHA256_C)
-void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *ssl, unsigned char hash[32] )
+void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *ssl, unsigned char *hash )
 {
     mbedtls_sha256_context sha256;
 
@@ -1240,7 +1240,7 @@ void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *ssl, unsigned char hash[32
 #endif /* MBEDTLS_SHA256_C */
 
 #if defined(MBEDTLS_SHA512_C)
-void ssl_calc_verify_tls_sha384( mbedtls_ssl_context *ssl, unsigned char hash[48] )
+void ssl_calc_verify_tls_sha384( mbedtls_ssl_context *ssl, unsigned char *hash )
 {
     mbedtls_sha512_context sha512;
 
@@ -6363,6 +6363,9 @@ static void ssl_calc_finished_tls_sha256(
 #endif /* MBEDTLS_SHA256_C */
 
 #if defined(MBEDTLS_SHA512_C)
+
+typedef int (*finish_sha384_t)(mbedtls_sha512_context*, unsigned char*);
+
 static void ssl_calc_finished_tls_sha384(
                 mbedtls_ssl_context *ssl, unsigned char *buf, int from )
 {
@@ -6370,6 +6373,12 @@ static void ssl_calc_finished_tls_sha384(
     const char *sender;
     mbedtls_sha512_context sha512;
     unsigned char padbuf[48];
+    /*
+     * For SHA-384, we can save 16 bytes by keeping padbuf 48 bytes long.
+     * However, to avoid stringop-overflow warning in gcc, we have to cast
+     * mbedtls_sha512_finish_ret().
+     */
+    finish_sha384_t finish_sha384 = (finish_sha384_t)mbedtls_sha512_finish_ret;
 
     mbedtls_ssl_session *session = ssl->session_negotiate;
     if( !session )
@@ -6396,7 +6405,7 @@ static void ssl_calc_finished_tls_sha384(
              ? "client finished"
              : "server finished";
 
-    mbedtls_sha512_finish_ret( &sha512, padbuf );
+    finish_sha384( &sha512, padbuf );
 
     ssl->handshake->tls_prf( session->master, 48, sender,
                              padbuf, 48, buf, len );
diff --git a/programs/test/selftest.c b/programs/test/selftest.c
index 9bc9a9c6b..fe35bb15a 100644
--- a/programs/test/selftest.c
+++ b/programs/test/selftest.c
@@ -185,7 +185,7 @@ static int calloc_self_test( int verbose )
 }
 #endif /* MBEDTLS_SELF_TEST */
 
-static int test_snprintf( size_t n, const char ref_buf[10], int ref_ret )
+static int test_snprintf( size_t n, const char *ref_buf, int ref_ret )
 {
     int ret;
     char buf[10] = "xxxxxxxxx";
diff --git a/tests/suites/host_test.function b/tests/suites/host_test.function
index ca51e7b28..1178135c5 100644
--- a/tests/suites/host_test.function
+++ b/tests/suites/host_test.function
@@ -330,7 +330,7 @@ static int convert_params( size_t cnt , char ** params , int * int_params_store
 #if defined(__GNUC__)
 __attribute__((__noinline__))
 #endif
-static int test_snprintf( size_t n, const char ref_buf[10], int ref_ret )
+static int test_snprintf( size_t n, const char *ref_buf, int ref_ret )
 {
     int ret;
     char buf[10] = "xxxxxxxxx";