diff --git a/include/mysql/client_plugin.h b/include/mysql/client_plugin.h
index ac29afd6..72939d24 100644
--- a/include/mysql/client_plugin.h
+++ b/include/mysql/client_plugin.h
@@ -78,7 +78,7 @@
   const char *license;                                  \
   void *mysql_api;                                      \
   int (*init)(char *, size_t, int, va_list);            \
-  int (*deinit)();                                      \
+  int (*deinit)(void);                                  \
   int (*options)(const char *option, const void *);
 struct st_mysql_client_plugin
 {
diff --git a/plugins/auth/caching_sha2_pw.c b/plugins/auth/caching_sha2_pw.c
index d4dc0fc6..e9762497 100644
--- a/plugins/auth/caching_sha2_pw.c
+++ b/plugins/auth/caching_sha2_pw.c
@@ -134,7 +134,7 @@ static int ma_sha256_scramble(unsigned char *scramble, size_t scramble_len,
 
 /* function prototypes */
 static int auth_caching_sha2_client(MYSQL_PLUGIN_VIO *vio, MYSQL *mysql);
-static int auth_caching_sha2_deinit();
+static int auth_caching_sha2_deinit(void);
 static int auth_caching_sha2_init(char *unused1,
     size_t unused2,
     int unused3,
@@ -450,7 +450,7 @@ static int auth_caching_sha2_init(char *unused1 __attribute__((unused)),
 /* }}} */
 
 /* {{{ auth_caching_sha2_deinit */
-static int auth_caching_sha2_deinit()
+static int auth_caching_sha2_deinit(void)
 {
 #if defined(HAVE_WINCRYPT)
   BCryptCloseAlgorithmProvider(Sha256Prov, 0);
diff --git a/plugins/auth/ed25519.c b/plugins/auth/ed25519.c
index 3b332057..ed36ab09 100644
--- a/plugins/auth/ed25519.c
+++ b/plugins/auth/ed25519.c
@@ -61,7 +61,7 @@ extern BCRYPT_ALG_HANDLE Sha512Prov;
 
 /* function prototypes */
 static int auth_ed25519_client(MYSQL_PLUGIN_VIO *vio, MYSQL *mysql);
-static int auth_ed25519_deinit();
+static int auth_ed25519_deinit(void);
 static int auth_ed25519_init(char *unused1,
     size_t unused2,
     int unused3,
@@ -132,7 +132,7 @@ static int auth_ed25519_init(char *unused1 __attribute__((unused)),
 /* }}} */
 
 /* {{{ auth_ed25519_deinit */
-static int auth_ed25519_deinit()
+static int auth_ed25519_deinit(void)
 {
 #if defined(HAVE_WINCRYPT)
   BCryptCloseAlgorithmProvider(Sha512Prov, 0);
diff --git a/plugins/trace/trace_example.c b/plugins/trace/trace_example.c
index 816b8c06..1060542c 100644
--- a/plugins/trace/trace_example.c
+++ b/plugins/trace/trace_example.c
@@ -212,7 +212,7 @@ static int trace_init(char *errormsg,
 }
 /* }}} */
 
-static int trace_deinit()
+static int trace_deinit(void)
 {
   /* unregister plugin */
   while(trace_info)