--- exim_monitor/em_log.c
+++ exim_monitor/em_log.c
@@ -58,6 +58,8 @@
 static int size = 0;
 static int top = 0;
 
+static void show_log(char *s, ...) PRINTF_FUNCTION(1,2);
+
 static void show_log(char *s, ...)
 {
 int length, newtop;
@@ -364,7 +366,7 @@
 if (log_datestamping)
   {
   uschar log_file_wanted[256];
-  string_format(log_file_wanted, sizeof(log_file_wanted), CS log_file);
+  string_format(log_file_wanted, sizeof(log_file_wanted), "%s", CS log_file);
   if (Ustrcmp(log_file_wanted, log_file_open) != 0)
     {
     if (LOG != NULL)
--- exim_monitor/em_main.c
+++ exim_monitor/em_main.c
@@ -656,7 +656,7 @@
 
 if (log_file[0] != 0)
   {
-  (void)string_format(log_file_open, sizeof(log_file_open), CS log_file);
+  (void)string_format(log_file_open, sizeof(log_file_open), "%s", CS log_file);
   log_datestamping = string_datestamp_offset >= 0;
 
   LOG = fopen(CS log_file_open, "r");
--- exim_monitor/em_text.c
+++ exim_monitor/em_text.c
@@ -60,6 +60,8 @@
 *           Display text from format             *
 *************************************************/
 
+void text_showf(Widget w, char *s, ...) PRINTF_FUNCTION(2,3);
+
 void text_showf(Widget w, char *s, ...)
 {
 va_list ap;
--- src/demime.c
+++ src/demime.c
@@ -823,7 +823,7 @@
     (void)string_vformat(US f, 16383,(char *)format, ap);
     va_end(ap);
     f-=22;
-    log_write(0, LOG_MAIN, f);
+    log_write(0, LOG_MAIN, "%s", f);
     /* then copy to demime_reason_buffer if new
     level is greater than old level */
     if (level > demime_errorlevel) {
--- src/dkim.c
+++ src/dkim.c
@@ -176,7 +176,7 @@
     }
 
     logmsg[ptr] = '\0';
-    log_write(0, LOG_MAIN, (char *)logmsg);
+    log_write(0, LOG_MAIN, "%s", (char *)logmsg);
 
     /* Build a colon-separated list of signing domains (and identities, if present) in dkim_signers */
     dkim_signers = string_append(dkim_signers,
--- src/exim_dbutil.c
+++ src/exim_dbutil.c
@@ -59,6 +59,7 @@
 #include "dbstuff.h"
 #include "osfunctions.h"
 #include "store.h"
+#include "local_scan.h"
 
 
 /* Identifiers for the different database types. */
--- src/functions.h
+++ src/functions.h
@@ -82,7 +82,7 @@
                   int, int, uschar *, bit_table *, int, uschar *, int);
 extern address_item *deliver_make_addr(uschar *, BOOL);
 extern int     deliver_message(uschar *, BOOL, BOOL);
-extern void    deliver_msglog(const char *, ...);
+extern void    deliver_msglog(const char *, ...) PRINTF_FUNCTION(1,2);
 extern void    deliver_set_expansions(address_item *);
 extern int     deliver_split_address(address_item *);
 extern void    deliver_succeeded(address_item *);
@@ -181,9 +181,9 @@
 extern uschar *moan_check_errorcopy(uschar *);
 extern BOOL    moan_skipped_syntax_errors(uschar *, error_block *, uschar *,
                  BOOL, uschar *);
-extern void    moan_smtp_batch(uschar *, char *, ...);
+extern void    moan_smtp_batch(uschar *, char *, ...) PRINTF_FUNCTION(2,3);
 extern void    moan_tell_someone(uschar *, address_item *, uschar *, char *,
-                 ...);
+                 ...) PRINTF_FUNCTION(4,5);
 extern BOOL    moan_to_sender(int, error_block *, header_line *, FILE *, BOOL);
 extern void    moan_write_from(FILE *);
 extern FILE   *modefopen(uschar *, char *, mode_t);
@@ -271,7 +271,7 @@
                  int *);
 extern void   *search_open(uschar *, int, int, uid_t *, gid_t *);
 extern void    search_tidyup(void);
-extern void    set_process_info(char *, ...);
+extern void    set_process_info(char *, ...) PRINTF_FUNCTION(1,2);
 extern void    sha1_end(sha1 *, const uschar *, int, uschar *);
 extern void    sha1_mid(sha1 *, const uschar *);
 extern void    sha1_start(sha1 *);
@@ -299,7 +299,7 @@
 extern BOOL    smtp_start_session(void);
 extern int     smtp_ungetc(int);
 extern BOOL    smtp_verify_helo(void);
-extern int     smtp_write_command(smtp_outblock *, BOOL, char *, ...);
+extern int     smtp_write_command(smtp_outblock *, BOOL, char *, ...) PRINTF_FUNCTION(3,4);
 #ifdef WITH_CONTENT_SCAN
 extern int     spam(uschar **);
 extern FILE   *spool_mbox(unsigned long *, uschar *);
@@ -321,13 +321,13 @@
 extern uschar *string_copylc(uschar *);
 extern uschar *string_copynlc(uschar *, int);
 extern uschar *string_dequote(uschar **);
-extern BOOL    string_format(uschar *, int, char *, ...);
+extern BOOL    string_format(uschar *, int, char *, ...) PRINTF_FUNCTION(3,4);
 extern uschar *string_format_size(int, uschar *);
 extern int     string_interpret_escape(uschar **);
 extern int     string_is_ip_address(uschar *, int *);
 extern uschar *string_log_address(address_item *, BOOL, BOOL);
 extern uschar *string_nextinlist(uschar **, int *, uschar *, int);
-extern uschar *string_open_failed(int, char *, ...);
+extern uschar *string_open_failed(int, char *, ...) PRINTF_FUNCTION(2,3);
 extern uschar *string_printing2(uschar *, BOOL);
 extern uschar *string_split_message(uschar *);
 extern BOOL    string_vformat(uschar *, int, char *, va_list);
--- src/local_scan.h
+++ src/local_scan.h
@@ -175,7 +175,7 @@
 extern void    header_remove(int, uschar *);
 extern BOOL    header_testname(header_line *, uschar *, int, BOOL);
 extern BOOL    header_testname_incomplete(header_line *, uschar *, int, BOOL);
-extern void    log_write(unsigned int, int, char *format, ...);
+extern void    log_write(unsigned int, int, char *format, ...) PRINTF_FUNCTION(3,4);
 extern int     lss_b64decode(uschar *, uschar **);
 extern uschar *lss_b64encode(uschar *, int);
 extern int     lss_match_domain(uschar *, uschar *);
@@ -190,6 +190,6 @@
 extern void    smtp_vprintf(char *, va_list);
 extern uschar *string_copy(uschar *);
 extern uschar *string_copyn(uschar *, int);
-extern uschar *string_sprintf(char *, ...);
+extern uschar *string_sprintf(char *, ...) PRINTF_FUNCTION(1,2);
 
 /* End of local_scan.h */