diff --git a/Makefile b/Makefile
index b2d5924b..894874ae 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 PROGS=notmuch
 
-CXXWARNINGS_FLAGS=-Wall -Wextra -Wwrite-strings
+CXXWARNINGS_FLAGS=-Wall -Wextra -Wmissing-declarations -Wwrite-strings
 CWARNINGS_FLAGS=$(CXXWARNINGS_FLAGS)
 
 CDEPENDS_FLAGS=`pkg-config --cflags glib-2.0 talloc`
diff --git a/database.cc b/database.cc
index cd057846..e1ea324d 100644
--- a/database.cc
+++ b/database.cc
@@ -519,7 +519,7 @@ notmuch_database_get_path (notmuch_database_t *notmuch)
     return notmuch->path;
 }
 
-notmuch_private_status_t
+static notmuch_private_status_t
 find_timestamp_document (notmuch_database_t *notmuch, const char *db_key,
 			 Xapian::Document *doc, unsigned int *doc_id)
 {
@@ -623,7 +623,7 @@ notmuch_database_get_timestamp (notmuch_database_t *notmuch, const char *key)
  *
  * Otherwise, returns a newly talloced string belonging to 'ctx'.
  */
-const char *
+static const char *
 _resolve_message_id_to_thread_id (notmuch_database_t *notmuch,
 				  void *ctx,
 				  const char *message_id)
diff --git a/message-file.c b/message-file.c
index f625a930..2bd56056 100644
--- a/message-file.c
+++ b/message-file.c
@@ -149,7 +149,7 @@ notmuch_message_file_restrict_headers (notmuch_message_file_t *message, ...)
     notmuch_message_file_restrict_headersv (message, va_headers);
 }
 
-void
+static void
 copy_header_unfolding (header_value_closure_t *value,
 		       const char *chunk)
 {
diff --git a/message.cc b/message.cc
index 75ec6349..5922cfcc 100644
--- a/message.cc
+++ b/message.cc
@@ -310,7 +310,7 @@ _notmuch_terms_destructor (notmuch_terms_t *terms)
     return 0;
 }
 
-notmuch_terms_t *
+static notmuch_terms_t *
 _notmuch_terms_create (void *ctx,
 		       Xapian::Document doc,
 		       const char *prefix_name)
@@ -526,7 +526,7 @@ notmuch_message_destroy (notmuch_message_t *message)
     talloc_free (message);
 }
 
-notmuch_bool_t
+static notmuch_bool_t
 _notmuch_terms_has_more (notmuch_terms_t *terms)
 {
     std::string s;
@@ -541,19 +541,19 @@ _notmuch_terms_has_more (notmuch_terms_t *terms)
 	return FALSE;
 }
 
-const char *
+static const char *
 _notmuch_terms_get (notmuch_terms_t *terms)
 {
     return talloc_strdup (terms, (*terms->iterator).c_str () + 1);
 }
 
-void
+static void
 _notmuch_terms_advance (notmuch_terms_t *terms)
 {
     terms->iterator++;
 }
 
-void
+static void
 _notmuch_terms_destroy (notmuch_terms_t *terms)
 {
     talloc_free (terms);
diff --git a/notmuch.c b/notmuch.c
index d98935bd..ef93ded9 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -87,14 +87,14 @@ chomp_newline (char *str)
 }
 
 /* Compute the number of seconds elapsed from start to end. */
-double
+static double
 tv_elapsed (struct timeval start, struct timeval end)
 {
     return ((end.tv_sec - start.tv_sec) +
 	    (end.tv_usec - start.tv_usec) / 1e6);
 }
 
-void
+static void
 print_formatted_seconds (double seconds)
 {
     int hours;
@@ -120,7 +120,7 @@ print_formatted_seconds (double seconds)
     printf ("%ds", (int) seconds);
 }
 
-void
+static void
 add_files_print_progress (add_files_state_t *state)
 {
     struct timeval tv_now;
@@ -165,7 +165,7 @@ add_files_print_progress (add_files_state_t *state)
  * The 'struct stat *st' must point to a structure that has already
  * been initialized for 'path' by calling stat().
  */
-notmuch_status_t
+static notmuch_status_t
 add_files_recursive (notmuch_database_t *notmuch,
 		     const char *path,
 		     struct stat *st,
@@ -332,7 +332,7 @@ add_files (notmuch_database_t *notmuch,
  * of path.  The result is added to *count (which should be
  * initialized to zero by the top-level caller before calling
  * count_files). */
-void
+static void
 count_files (const char *path, int *count)
 {
     DIR *dir;
@@ -400,7 +400,7 @@ count_files (const char *path, int *count)
     closedir (dir);
 }
 
-int
+static int
 setup_command (unused (int argc), unused (char *argv[]))
 {
     notmuch_database_t *notmuch = NULL;
@@ -526,7 +526,7 @@ setup_command (unused (int argc), unused (char *argv[]))
     return ret;
 }
 
-int
+static int
 new_command (unused (int argc), unused (char *argv[]))
 {
     notmuch_database_t *notmuch;
@@ -596,7 +596,7 @@ new_command (unused (int argc), unused (char *argv[]))
     return ret;
 }
 
-int
+static int
 search_command (int argc, char *argv[])
 {
     void *local = talloc_new (NULL);
@@ -668,14 +668,14 @@ search_command (int argc, char *argv[])
     return ret;
 }
 
-int
+static int
 show_command (unused (int argc), unused (char *argv[]))
 {
     fprintf (stderr, "Error: show is not implemented yet.\n");
     return 1;
 }
 
-int
+static int
 dump_command (int argc, char *argv[])
 {
     FILE *output;
@@ -751,7 +751,7 @@ dump_command (int argc, char *argv[])
     return ret;
 }
 
-int
+static int
 restore_command (int argc, char *argv[])
 {
     FILE *input;
@@ -892,7 +892,7 @@ command_t commands[] = {
       "\t\tRestore the tags from the given dump file (see 'dump')." }
 };
 
-void
+static void
 usage (void)
 {
     command_t *command;