diff --git a/configure b/configure
index f771bd074..d92a1172b 100755
--- a/configure
+++ b/configure
@@ -5229,6 +5229,54 @@ ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
+ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether C compiler accepts -Wformat-nonliteral" >&5
+$as_echo_n "checking whether C compiler accepts -Wformat-nonliteral... " >&6; }
+if ${ax_cv_check_cflags__Werror___Wformat_nonliteral+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+  ax_check_save_flags=$CFLAGS
+  CFLAGS="$CFLAGS -Werror  -Wformat-nonliteral"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  ax_cv_check_cflags__Werror___Wformat_nonliteral=yes
+else
+  ax_cv_check_cflags__Werror___Wformat_nonliteral=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+  CFLAGS=$ax_check_save_flags
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ax_cv_check_cflags__Werror___Wformat_nonliteral" >&5
+$as_echo "$ax_cv_check_cflags__Werror___Wformat_nonliteral" >&6; }
+if test x"$ax_cv_check_cflags__Werror___Wformat_nonliteral" = xyes; then :
+  CFLAGS="$CFLAGS -Wformat-nonliteral"
+else
+  :
+fi
+
+  ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
diff --git a/configure.ac b/configure.ac
index b2b143fd2..2917e4189 100644
--- a/configure.ac
+++ b/configure.ac
@@ -195,6 +195,8 @@ CFLAGS="$CFLAGS -Wall"
 dnl More warnings (if the compiler supports it):
 check_cc_flag([-Wextra], [CFLAGS="$CFLAGS -Wextra"])
 check_cc_flag([-Waggregate-return], [CFLAGS="$CFLAGS -Waggregate-return"])
+check_cc_flag([-Wformat-nonliteral], [CFLAGS="$CFLAGS -Wformat-nonliteral"])
+
 dnl The following few are more experimental, if they have false positives we'll have
 dnl to disable them:
 dnl Can't use this, too bad: check_cc_flag([-Wlogical-op], [CFLAGS="$CFLAGS -Wlogical-op"])
diff --git a/include/h.h b/include/h.h
index eeae45c66..f16635f2d 100644
--- a/include/h.h
+++ b/include/h.h
@@ -1024,7 +1024,7 @@ extern void user_account_login(MessageTag *recv_mtags, Client *client);
 extern void link_generator(void);
 extern void update_throttling_timer_settings(void);
 extern int hide_idle_time(Client *client, Client *target);
-extern void lost_server_link(Client *serv, FORMAT_STRING(const char *fmt), ...);
+extern void lost_server_link(Client *serv, FORMAT_STRING(const char *fmt), ...) __attribute__((format(printf,2,3)));
 extern char *sendtype_to_cmd(SendType sendtype);
 extern MODVAR MessageTagHandler *mtaghandlers;
 extern int security_group_valid_name(char *name);
@@ -1089,7 +1089,7 @@ extern char *log_type_valtostring(LogType v);
 #else
 #define unreal_log(...) do_unreal_log(__VA_ARGS__, NULL)
 #endif
-extern void do_unreal_log(LogLevel loglevel, char *subsystem, char *event_id, Client *client, char *msg, ...);
+extern void do_unreal_log(LogLevel loglevel, char *subsystem, char *event_id, Client *client, char *msg, ...) __attribute__((format(printf,5,0)));
 extern LogData *log_data_string(const char *key, const char *str);
 extern LogData *log_data_integer(const char *key, int64_t integer);
 extern LogData *log_data_client(const char *key, Client *client);
diff --git a/include/ircsprintf.h b/include/ircsprintf.h
index fe7876761..af308083d 100644
--- a/include/ircsprintf.h
+++ b/include/ircsprintf.h
@@ -17,7 +17,7 @@
 # define FORMAT_STRING(p) p
 #endif
 
-extern char *ircvsnprintf(char *str, size_t size, const char *format, va_list);
+extern char *ircvsnprintf(char *str, size_t size, const char *format, va_list) __attribute__((format(printf,3,0)));
 extern char *ircsnprintf(char *str, size_t size, FORMAT_STRING(const char *format), ...) __attribute__((format(printf,3,4)));
 
 #endif
diff --git a/src/ircd.c b/src/ircd.c
index 46539af69..dbf18dd18 100644
--- a/src/ircd.c
+++ b/src/ircd.c
@@ -502,21 +502,6 @@ char chess[] = {
 	85, 110, 114, 101, 97, 108, 0
 };
 
-static void version_check_logerror(char *fmt, ...)
-{
-va_list va;
-char buf[1024];
-
-	va_start(va, fmt);
-	vsnprintf(buf, sizeof(buf), fmt, va);
-	va_end(va);
-#ifndef _WIN32
-	fprintf(stderr, "[!!!] %s\n", buf);
-#else
-	win_log("[!!!] %s", buf);
-#endif
-}
-
 extern void applymeblock(void);
 
 extern MODVAR Event *events;
diff --git a/src/log.c b/src/log.c
index 2760774de..26694ae62 100644
--- a/src/log.c
+++ b/src/log.c
@@ -319,6 +319,8 @@ char *loglevel_to_string(LogLevel loglevel)
 	}
 }
 
+#define validvarcharacter(x)	(isalnum((x)) || ((x) == '_'))
+
 /** Build a string and replace $variables where needed.
  * See src/modules/blacklist.c for an example.
  * @param inbuf		The input string
@@ -351,7 +353,7 @@ void buildlogstring(const char *inbuf, char *outbuf, size_t len, json_t *details
 			if (*i == '$')
 				goto literal;
 
-			if (!isalnum(*i))
+			if (!validvarcharacter(*i))
 			{
 				/* What do we do with things like '$/' ? -- treat literal */
 				i--;
@@ -359,7 +361,7 @@ void buildlogstring(const char *inbuf, char *outbuf, size_t len, json_t *details
 			}
 
 			/* find termination */
-			for (p=i; isalnum(*p) || ((*p == '.') && isalnum(p[1])); p++);
+			for (p=i; validvarcharacter(*p) || ((*p == '.') && validvarcharacter(p[1])); p++);
 
 			/* find variable name in list */
 			*varname = '\0';
diff --git a/src/misc.c b/src/misc.c
index c3a7aff17..277b1b429 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -114,8 +114,8 @@ void ircd_log(int flags, FORMAT_STRING(const char *format), ...)
 	ircvsnprintf(buf, sizeof(buf), format, vl);
 	va_end(vl);
 
-	// FIXME: escape 'buf' !!!
-	do_unreal_log(ULOG_ERROR, "unknown", "UNKNOWN", NULL, buf, NULL);
+	// This is a stupid escape trick, we better use a different method / other function
+	unreal_log(ULOG_ERROR, "unknown", "UNKNOWN", NULL, "$_data", log_data_string("_data", buf));
 }
 
 /** Returns the date in rather long string */
diff --git a/src/modules/stats.c b/src/modules/stats.c
index ad0ca147f..5520b14fc 100644
--- a/src/modules/stats.c
+++ b/src/modules/stats.c
@@ -1035,11 +1035,11 @@ int stats_linkinfoall(Client *client, char *para)
 int stats_linkinfoint(Client *client, char *para, int all)
 {
 #ifndef DEBUGMODE
-	static char Sformat[] = "SendQ SendM SendBytes RcveM RcveBytes Open_since :Idle";
-	static char Lformat[] = "%s%s %u %u %u %u %u %u :%u";
+	#define Sformat "SendQ SendM SendBytes RcveM RcveBytes Open_since :Idle"
+	#define Lformat "%s%s %u %u %u %u %u %lld :%lld"
 #else
-	static char Sformat[] = "SendQ SendM SendBytes RcveM RcveBytes Open_since CPU :Idle";
-	static char Lformat[] = "%s%s %u %u %u %u %u %u %s";
+	#define Sformat "SendQ SendM SendBytes RcveM RcveBytes Open_since CPU :Idle"
+	#define Lformat "%s%s %u %u %u %u %u %lld %s"
 	char pbuf[96];		/* Should be enough for to ints */
 #endif
 	int remote = 0;
@@ -1090,8 +1090,9 @@ int stats_linkinfoint(Client *client, char *para, int all)
 		}
 
 #ifdef DEBUGMODE
-		ircsnprintf(pbuf, sizeof(pbuf), "%ld :%ld", (long)acptr->local->cputime,
-		      (long)(acptr->user && MyConnect(acptr)) ? TStime() - acptr->local->last : 0);
+		ircsnprintf(pbuf, sizeof(pbuf), "%lld :%lld",
+			(long long)acptr->local->cputime,
+			(long long)((acptr->user && MyConnect(acptr)) ? TStime() - acptr->local->last : 0));
 #endif
 		if (ValidatePermissionsForPath("server:info:stats",client,NULL,NULL,NULL))
 		{
@@ -1104,10 +1105,9 @@ int stats_linkinfoint(Client *client, char *para, int all)
 				(int)acptr->local->sendM, (int)acptr->local->sendK,
 				(int)acptr->local->receiveM,
 				(int)acptr->local->receiveK,
-			 	TStime() - acptr->local->firsttime,
+				(long long)(TStime() - acptr->local->firsttime),
 #ifndef DEBUGMODE
-				(acptr->user && MyConnect(acptr)) ?
-				TStime() - acptr->local->last : 0);
+				(long long)((acptr->user && MyConnect(acptr)) ? TStime() - acptr->local->last : 0));
 #else
 				pbuf);
 #endif
@@ -1123,10 +1123,9 @@ int stats_linkinfoint(Client *client, char *para, int all)
 				(int)acptr->local->sendM, (int)acptr->local->sendK,
 				(int)acptr->local->receiveM,
 				(int)acptr->local->receiveK,
-				TStime() - acptr->local->firsttime,
+				(long long)((TStime() - acptr->local->firsttime)),
 #ifndef DEBUGMODE
-				(acptr->user && MyConnect(acptr)) ?
-				TStime() - acptr->local->last : 0);
+				(long long)((acptr->user && MyConnect(acptr)) ? TStime() - acptr->local->last : 0));
 #else
 				pbuf);
 #endif
diff --git a/src/modules/whox.c b/src/modules/whox.c
index 5866ee376..da0bd4f12 100644
--- a/src/modules/whox.c
+++ b/src/modules/whox.c
@@ -84,6 +84,7 @@ static int convert_classical_who_request(Client *client, int *parc, char *parv[]
 char *whox_md_serialize(ModData *m);
 void whox_md_unserialize(char *str, ModData *m);
 void whox_md_free(ModData *md);
+static void append_format(char *buf, size_t bufsize, size_t *pos, const char *fmt, ...) __attribute__((format(printf,4,5)));
 
 MOD_INIT()
 {
diff --git a/src/send.c b/src/send.c
index b146cbf12..5515da797 100644
--- a/src/send.c
+++ b/src/send.c
@@ -26,10 +26,13 @@
 
 #include "unrealircd.h"
 
+/* Temporarily ignore these for this entire file. FIXME later: */
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+
 /* Some forward declarions are needed */
-void vsendto_one(Client *to, MessageTag *mtags, const char *pattern, va_list vl);
-void vsendto_prefix_one(Client *to, Client *from, MessageTag *mtags, const char *pattern, va_list vl);
-static int vmakebuf_local_withprefix(char *buf, size_t buflen, Client *from, const char *pattern, va_list vl);
+void vsendto_one(Client *to, MessageTag *mtags, const char *pattern, va_list vl) __attribute__((format(printf,3,0)));
+void vsendto_prefix_one(Client *to, Client *from, MessageTag *mtags, const char *pattern, va_list vl) __attribute__((format(printf,4,0)));
+static int vmakebuf_local_withprefix(char *buf, size_t buflen, Client *from, const char *pattern, va_list vl) __attribute__((format(printf,4,0)));
 
 #define ADD_CRLF(buf, len) { if (len > 510) len = 510; \
                              buf[len++] = '\r'; buf[len++] = '\n'; buf[len] = '\0'; } while(0)
diff --git a/src/serv.c b/src/serv.c
index 703052c7c..816920d3d 100644
--- a/src/serv.c
+++ b/src/serv.c
@@ -61,6 +61,10 @@ extern MOTDLine *find_file(char *, short);
 
 void reread_motdsandrules();
 
+/* Temporarily ignore for this function. FIXME later!!! */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+
 /** Send a message upstream if necessary and check if it's for us.
  * @param client	The sender
  * @param mtags		Message tags associated with this message
@@ -117,6 +121,8 @@ int hunt_server(Client *client, MessageTag *mtags, char *command, int server, in
 	return HUNTED_PASS;
 }
 
+#pragma GCC diagnostic pop
+
 #ifndef _WIN32
 /** Grab operating system name on Windows (outdated) */
 char *getosname(void)
diff --git a/src/socket.c b/src/socket.c
index d850de6c6..cfb3911d2 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -28,6 +28,9 @@
 #include "unrealircd.h"
 #include "dns.h"
 
+/* Temporarily ignore these for this entire file. FIXME later: */
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
+
 int OpenFiles = 0;    /* GLOBAL - number of files currently open */
 int readcalls = 0;
 
diff --git a/src/unrealdb.c b/src/unrealdb.c
index e8a722658..d6b551314 100644
--- a/src/unrealdb.c
+++ b/src/unrealdb.c
@@ -68,6 +68,7 @@
 /* Forward declarations - only used for internal (static) functions, of course */
 static SecretCache *find_secret_cache(Secret *secr, UnrealDBConfig *cfg);
 static void unrealdb_add_to_secret_cache(Secret *secr, UnrealDBConfig *cfg);
+static void unrealdb_set_error(UnrealDB *c, UnrealDBError errcode, FORMAT_STRING(const char *pattern), ...) __attribute__((format(printf,3,4)));
 
 UnrealDBError unrealdb_last_error_code;
 static char *unrealdb_last_error_string = NULL;
@@ -934,6 +935,7 @@ int unrealdb_read_char(UnrealDB *c, char *t)
 
 /** @} */
 
+#if 0
 void fatal_error(FORMAT_STRING(const char *pattern), ...)
 {
 	va_list vl;
@@ -1045,6 +1047,7 @@ void unrealdb_test(void)
 	fprintf(stderr, "**** TESTING UNENCRYPTED ****\n");
 	unrealdb_test_speed(NULL);
 }
+#endif
 
 /** TODO: document and implement
  */