diff --git a/CMakeLists.txt b/CMakeLists.txt
index 97fac89f..178999cd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -134,7 +134,7 @@ SET(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} -DDBUG_OFF
 
 IF(CMAKE_COMPILER_IS_GNUCC)
   INCLUDE(CheckCCompilerFlag)
-  SET(GCC_FLAGS -Wunused -Wno-uninitialized  -Wall -Wextra -Wformat-security -Wno-init-self -Wwrite-strings -Wshift-count-overflow -Wdeclaration-after-statement)
+  SET(GCC_FLAGS -Wunused -Wlogical-op -Wno-uninitialized  -Wall -Wextra -Wformat-security -Wno-init-self -Wwrite-strings -Wshift-count-overflow -Wdeclaration-after-statement)
   FOREACH(GCC_FLAG ${GCC_FLAGS})
     CHECK_C_COMPILER_FLAG("${GCC_FLAG}" HAS_${GCC_FLAG}_FLAG)
     IF(${HAS_${GCC_FLAG}_FLAG})
diff --git a/include/ma_config.h.in b/include/ma_config.h.in
index 60fb77b7..c25662fa 100644
--- a/include/ma_config.h.in
+++ b/include/ma_config.h.in
@@ -163,103 +163,103 @@
  */
 /* Types we may use */
 #cmakedefine SIZEOF_CHAR @SIZEOF_CHAR@
-#if SIZEOF_CHAR
+#if defined(SIZEOF_CHAR)
 # define HAVE_CHAR 1
 #endif
 
 #cmakedefine SIZEOF_CHARP @SIZEOF_CHARP@
-#if SIZEOF_CHARP
+#if defined(SIZEOF_CHARP)
 # define HAVE_CHARP 1
 #endif
 
 #cmakedefine SIZEOF_SHORT @SIZEOF_SHORT@
-#if SIZEOF_SHORT
+#if defined(SIZEOF_SHORT)
 # define HAVE_SHORT 1
 #endif
 
 #cmakedefine SIZEOF_INT @SIZEOF_INT@
-#if SIZEOF_INT
+#if defined(SIZEOF_INT)
 # define HAVE_INT 1
 #endif
 
 #cmakedefine SIZEOF_LONG @SIZEOF_LONG@
-#if SIZEOF_LONG
+#if defined(SIZEOF_LONG)
 # define HAVE_LONG 1
 #endif
 
 #cmakedefine SIZEOF_LONG_LONG @SIZEOF_LONG_LONG@
-#if SIZEOF_LONG_LONG
+#if defined(SIZEOF_LONG_LONG)
 # define HAVE_LONG_LONG 1
 #endif
 
 
 #cmakedefine SIZEOF_SIGSET_T @SIZEOF_SIGSET_T@
-#if SIZEOF_SIGSET_T
+#if defined(SIZEOF_SIGSET_T)
 # define HAVE_SIGSET_T 1
 #endif
 
 #cmakedefine SIZEOF_SIZE_T @SIZEOF_SIZE_T@
-#if SIZEOF_SIZE_T
+#if defined(SIZEOF_SIZE_T)
 # define HAVE_SIZE_T 1
 #endif
 
 #cmakedefine SIZEOF_UCHAR @SIZEOF_UCHAR@
-#if SIZEOF_UCHAR
+#if defined(SIZEOF_UCHAR)
 # define HAVE_UCHAR 1
 #endif
 
 #cmakedefine SIZEOF_UINT @SIZEOF_UINT@
-#if SIZEOF_UINT
+#if defined(SIZEOF_UINT)
 # define HAVE_UINT 1
 #endif
 
 #cmakedefine SIZEOF_ULONG @SIZEOF_ULONG@
-#if SIZEOF_ULONG
+#if defined(SIZEOF_ULONG)
 # define HAVE_ULONG 1
 #endif
 
 #cmakedefine SIZEOF_INT8 @SIZEOF_INT8@
-#if SIZEOF_INT8
+#if defined(SIZEOF_INT8)
 # define HAVE_INT8 1
 #endif
 #cmakedefine SIZEOF_UINT8 @SIZEOF_UINT8@
-#if SIZEOF_UINT8
+#if defined(SIZEOF_UINT8)
 # define HAVE_UINT8 1
 #endif
 
 #cmakedefine SIZEOF_INT16 @SIZEOF_INT16@
-#if SIZEOF_INT16
+#if defined(SIZEOF_INT16)
 # define HAVE_INT16 1
 #endif
 #cmakedefine SIZEOF_UINT16 @SIZEOF_UINT16@
-#if SIZEOF_UINT16
+#if defined(SIZEOF_UINT16)
 # define HAVE_UINT16 1
 #endif
 
 #cmakedefine SIZEOF_INT32 @SIZEOF_INT32@
-#if SIZEOF_INT32
+#if defined(SIZEOF_INT32)
 # define HAVE_INT32 1
 #endif
 #cmakedefine SIZEOF_UINT32 @SIZEOF_UINT32@
-#if SIZEOF_UINT32
+#if defined(SIZEOF_UINT32)
 # define HAVE_UINT32 1
 #endif
 #cmakedefine SIZEOF_U_INT32_T @SIZEOF_U_INT32_T@
-#if SIZEOF_U_INT32_T
+#if defined(SIZEOF_U_INT32_T)
 # define HAVE_U_INT32_T 1
 #endif
 
 #cmakedefine SIZEOF_INT64 @SIZEOF_INT64@
-#if SIZEOF_INT64
+#if defined(SIZEOF_INT64)
 # define HAVE_INT64 1
 #endif
 #cmakedefine SIZEOF_UINT64 @SIZEOF_UINT64@
-#if SIZEOF_UINT64
+#if defined(SIZEOF_UINT64)
 # define HAVE_UINT64 1
 #endif
 
 #cmakedefine SIZEOF_SOCKLEN_T @SIZEOF_SOCKLEN_T@
-#if SIZEOF_SOCKLEN_T
+#if defined(SIZEOF_SOCKLEN_T)
 # define HAVE_SOCKLEN_T 1
 #endif
 
diff --git a/include/ma_global.h b/include/ma_global.h
index ce96b002..819a8273 100644
--- a/include/ma_global.h
+++ b/include/ma_global.h
@@ -185,11 +185,11 @@ double my_ulonglong2double(unsigned long long A);
 #ifdef HAVE_FCNTL_H
 #include <fcntl.h>
 #endif
-#if TIME_WITH_SYS_TIME
+#if defined(TIME_WITH_SYS_TIME)
 # include <sys/time.h>
 # include <time.h>
 #else
-# if HAVE_SYS_TIME_H
+# if defined(HAVE_SYS_TIME_H)
 #  include <sys/time.h>
 # else
 #  include <time.h>
@@ -671,7 +671,7 @@ typedef ulonglong uint64;
   The following is done with a if to not get problems with pre-processors
   with late define evaluation
 */
-#if SIZEOF_OFF_T == 4
+#if defined(SIZEOF_OFF_T) && SIZEOF_OFF_T == 4
 #define SYSTEM_SIZEOF_OFF_T 4
 #else
 #define SYSTEM_SIZEOF_OFF_T 8
@@ -682,7 +682,7 @@ typedef ulonglong uint64;
 #define SYSTEM_SIZEOF_OFF_T SIZEOF_OFF_T
 #endif /* USE_RAID */
 
-#if SIZEOF_OFF_T > 4
+#if defined(SIZEOF_OFF_T) && SIZEOF_OFF_T > 4
 typedef ulonglong my_off_t;
 #else
 typedef unsigned long my_off_t;
diff --git a/libmariadb/ma_charset.c b/libmariadb/ma_charset.c
index 81c6a554..a3e09430 100644
--- a/libmariadb/ma_charset.c
+++ b/libmariadb/ma_charset.c
@@ -259,7 +259,7 @@ static unsigned int mysql_mbcharlen_utf8(unsigned int utf8)
 
 static unsigned int check_mb_big5(const char *start, const char *end)
 {
-  return (valid_big5head(*(start)) && (end - start) > 1 && valid_big5tail(*(start + 1)) ? 2 : 0);
+  return (valid_big5head(*((const uchar*) start)) && (end - start) > 1 && valid_big5tail(*((const uchar*) start + 1)) ? 2 : 0);
 }
 
 
diff --git a/libmariadb/mariadb_lib.c b/libmariadb/mariadb_lib.c
index 8b79747c..35474371 100644
--- a/libmariadb/mariadb_lib.c
+++ b/libmariadb/mariadb_lib.c
@@ -507,7 +507,7 @@ void read_user_name(char *name)
 	str="UNKNOWN_USER";
     }
     ma_strmake(name,str,USERNAME_LENGTH);
-#elif HAVE_CUSERID
+#elif defined(HAVE_CUSERID)
     (void) cuserid(name);
 #else
     ma_strmake(name,"UNKNOWN_USER", USERNAME_LENGTH);
diff --git a/libmariadb/secure/openssl.c b/libmariadb/secure/openssl.c
index 56e6bb38..04cbeebf 100644
--- a/libmariadb/secure/openssl.c
+++ b/libmariadb/secure/openssl.c
@@ -42,7 +42,7 @@
 #ifdef HAVE_TLS_SESSION_CACHE
 #undef HAVE_TLS_SESSION_CACHE
 #endif
-#if OPENSSL_USE_BIOMETHOD
+#if defined(OPENSSL_USE_BIOMETHOD)
 #undef OPENSSL_USE_BIOMETHOD
 #endif
 #ifndef HAVE_OPENSSL_DEFAULT
@@ -69,7 +69,7 @@ static pthread_mutex_t LOCK_openssl_config;
 #ifndef HAVE_OPENSSL_1_1_API
 static pthread_mutex_t *LOCK_crypto= NULL;
 #endif
-#if OPENSSL_USE_BIOMETHOD
+#if defined(OPENSSL_USE_BIOMETHOD)
 static int ma_bio_read(BIO *h, char *buf, int size);
 static int ma_bio_write(BIO *h, const char *buf, int size);
 static BIO_METHOD ma_BIO_method;
@@ -350,7 +350,7 @@ int ma_tls_start(char *errmsg __attribute__((unused)), size_t errmsg_len __attri
   OpenSSL_add_all_algorithms();
 #endif
   disable_sigpipe();
-#if OPENSSL_USE_BIOMETHOD
+#ifdef OPENSSL_USE_BIOMETHOD
   memcpy(&ma_BIO_method, BIO_s_socket(), sizeof(BIO_METHOD));
   ma_BIO_method.bread= ma_bio_read;
   ma_BIO_method.bwrite= ma_bio_write;
@@ -582,7 +582,7 @@ my_bool ma_tls_connect(MARIADB_TLS *ctls)
   MYSQL *mysql;
   MARIADB_PVIO *pvio;
   int rc;
-#if OPENSSL_USE_BIOMETHOD
+#ifdef OPENSSL_USE_BIOMETHOD
   BIO_METHOD *bio_method= NULL;
   BIO *bio;
 #endif
@@ -596,7 +596,7 @@ my_bool ma_tls_connect(MARIADB_TLS *ctls)
 
   SSL_clear(ssl);
 
-#if OPENSSL_USE_BIOMETHOD
+#ifdef OPENSSL_USE_BIOMETHOD
   bio= BIO_new(&ma_BIO_method);
   bio->ptr= pvio;
   SSL_set_bio(ssl, bio, bio);