diff --git a/lib-src/etags.c b/lib-src/etags.c
index 84dfa527e98..03bc55de03d 100644
--- a/lib-src/etags.c
+++ b/lib-src/etags.c
@@ -705,7 +705,7 @@ and optionally Prolog-like definitions (first rule for a predicate or \
 function).\n\
 To enable this behavior, run etags using --declarations.";
 static bool with_mercury_definitions = false;
-float mercury_heuristics_ratio = MERCURY_HEURISTICS_RATIO;
+static float mercury_heuristics_ratio = MERCURY_HEURISTICS_RATIO;
 
 static const char *Objc_suffixes [] =
   { "lm",			/* Objective lex file  */
diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index ac4f320f9a5..ee589e03397 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -660,11 +660,11 @@ close_emacs_globals (ptrdiff_t num_symbols)
   printf (("};\n"
 	   "extern struct emacs_globals globals;\n"
 	   "\n"
-	   "#ifndef DEFINE_SYMBOLS\n"
-	   "extern\n"
-	   "#endif\n"
-	   "struct Lisp_Symbol lispsym[%td];\n"),
-	  num_symbols);
+	   "extern struct Lisp_Symbol lispsym[%td];\n"
+	   "#ifdef DEFINE_SYMBOLS\n"
+	   "struct Lisp_Symbol lispsym[%td];\n"
+	   "#endif\n"),
+	  num_symbols, num_symbols);
 }
 
 static void
diff --git a/src/alloc.c b/src/alloc.c
index 4226cb1d1a0..28e32554472 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -8338,7 +8338,7 @@ enum defined_HAVE_PGTK { defined_HAVE_PGTK = false };
    then xbacktrace could fail.  Similarly for the other enums and
    their values.  Some non-GCC compilers don't like these constructs.  */
 #ifdef __GNUC__
-union
+extern union enums_for_gdb
 {
   enum CHARTAB_SIZE_BITS CHARTAB_SIZE_BITS;
   enum char_table_specials char_table_specials;
@@ -8353,5 +8353,6 @@ union
   enum pvec_type pvec_type;
   enum defined_HAVE_X_WINDOWS defined_HAVE_X_WINDOWS;
   enum defined_HAVE_PGTK defined_HAVE_PGTK;
-} const EXTERNALLY_VISIBLE gdb_make_enums_visible = {0};
+} const gdb_make_enums_visible;
+union enums_for_gdb const EXTERNALLY_VISIBLE gdb_make_enums_visible = {0};
 #endif	/* __GNUC__ */
diff --git a/src/emacs.c b/src/emacs.c
index 22da39a4d1c..58c751eaa6a 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -166,6 +166,7 @@ static const char emacs_copyright[] = COPYRIGHT;
 static const char emacs_bugreport[] = PACKAGE_BUGREPORT;
 
 /* Put version info into the executable in the form that 'ident' uses.  */
+extern char const RCS_Id[];
 char const EXTERNALLY_VISIBLE RCS_Id[]
   = "$Id" ": GNU Emacs " PACKAGE_VERSION
     " (" EMACS_CONFIGURATION " " EMACS_CONFIG_FEATURES ") $";
diff --git a/src/keyboard.c b/src/keyboard.c
index bd1bb3bb4be..2995b3f906c 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -3650,6 +3650,7 @@ readable_events (int flags)
 }
 
 /* Set this for debugging, to have a way to get out */
+extern int stop_character;
 int stop_character EXTERNALLY_VISIBLE;
 
 static KBOARD *
diff --git a/src/lisp.h b/src/lisp.h
index 010d63e4dd9..41f8af35e8a 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -55,7 +55,8 @@ INLINE_HEADER_BEGIN
 
 #define DECLARE_GDB_SYM(type, id) type const id EXTERNALLY_VISIBLE
 #ifdef MAIN_PROGRAM
-# define DEFINE_GDB_SYMBOL_BEGIN(type, id) DECLARE_GDB_SYM (type, id)
+# define DEFINE_GDB_SYMBOL_BEGIN(type, id) \
+   extern DECLARE_GDB_SYM (type, id); DECLARE_GDB_SYM (type, id)
 # define DEFINE_GDB_SYMBOL_END(id) = id;
 #else
 # define DEFINE_GDB_SYMBOL_BEGIN(type, id) extern DECLARE_GDB_SYM (type, id)
@@ -4435,6 +4436,7 @@ extern void parse_str_as_multibyte (const unsigned char *, ptrdiff_t,
 				    ptrdiff_t *, ptrdiff_t *);
 
 /* Defined in alloc.c.  */
+extern intptr_t garbage_collection_inhibited;
 extern void *my_heap_start (void);
 extern void check_pure_size (void);
 unsigned char *resize_string_data (Lisp_Object, ptrdiff_t, int, int);
diff --git a/src/pgtkselect.c b/src/pgtkselect.c
index b0ab15c6069..271411b87ca 100644
--- a/src/pgtkselect.c
+++ b/src/pgtkselect.c
@@ -353,7 +353,7 @@ struct pgtk_selection_request
 /* Stack of selections currently being processed.
    NULL if all requests have been fully processed.  */
 
-struct pgtk_selection_request *selection_request_stack;
+static struct pgtk_selection_request *selection_request_stack;
 
 static void
 pgtk_push_current_selection_request (struct selection_input_event *se,
diff --git a/src/print.c b/src/print.c
index 612d63b7e94..7aacd2b2e90 100644
--- a/src/print.c
+++ b/src/print.c
@@ -90,6 +90,7 @@ static ptrdiff_t print_number_index;
 static void print_interval (INTERVAL interval, void *pprintcharfun);
 
 /* GDB resets this to zero on W32 to disable OutputDebugString calls.  */
+extern bool print_output_debug_flag;
 bool print_output_debug_flag EXTERNALLY_VISIBLE = 1;
 
 
diff --git a/src/xdisp.c b/src/xdisp.c
index a7cae804006..4b7d7e02c68 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13195,8 +13195,6 @@ truncate_message_1 (void *a1, Lisp_Object a2)
   return false;
 }
 
-extern intptr_t garbage_collection_inhibited;
-
 /* Set the current message to STRING.  */
 
 static void
diff --git a/src/xselect.c b/src/xselect.c
index fd0f06eeed9..6578358adc0 100644
--- a/src/xselect.c
+++ b/src/xselect.c
@@ -562,12 +562,12 @@ struct x_selection_request
 /* Stack of selections currently being processed.
    NULL if all requests have been fully processed.  */
 
-struct x_selection_request *selection_request_stack;
+static struct x_selection_request *selection_request_stack;
 
 /* List of all outstanding selection transfers which are currently
    being processed.  */
 
-struct transfer outstanding_transfers;
+static struct transfer outstanding_transfers;
 
 /* A counter for selection serials.  */
 
diff --git a/src/xterm.c b/src/xterm.c
index 33ef18d8da5..11ef9a4bd94 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -971,7 +971,7 @@ struct x_selection_request_event
    selection requests inside long-lasting modal event loops, such as
    the drag-and-drop loop.  */
 
-struct x_selection_request_event *pending_selection_requests;
+static struct x_selection_request_event *pending_selection_requests;
 
 struct x_atom_ref
 {
@@ -1274,7 +1274,7 @@ static int x_dnd_waiting_for_motif_finish;
 
 /* The display the Motif drag receiver will send response data
    from.  */
-struct x_display_info *x_dnd_waiting_for_motif_finish_display;
+static struct x_display_info *x_dnd_waiting_for_motif_finish_display;
 
 /* Whether or not F1 was pressed during the drag-and-drop operation.
 
@@ -31921,8 +31921,6 @@ x_activate_timeout_atimer (void)
 
 /* Set up use of X before we make the first connection.  */
 
-extern frame_parm_handler x_frame_parm_handlers[];
-
 static struct redisplay_interface x_redisplay_interface =
   {
     x_frame_parm_handlers,
diff --git a/src/xterm.h b/src/xterm.h
index 437ef281b0c..bf402de326b 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -1727,6 +1727,7 @@ SELECTION_EVENT_DISPLAY (struct selection_input_event *ev)
 
 /* From xfns.c.  */
 
+extern frame_parm_handler x_frame_parm_handlers[];
 extern void x_free_gcs (struct frame *);
 extern void x_relative_mouse_position (struct frame *, int *, int *);
 extern void x_real_pos_and_offsets (struct frame *, int *, int *, int *,