diff --git a/src/include/access/rewriteheap.h b/src/include/access/rewriteheap.h
index aa5c48f219..3e27790b3f 100644
--- a/src/include/access/rewriteheap.h
+++ b/src/include/access/rewriteheap.h
@@ -52,6 +52,6 @@ typedef struct LogicalRewriteMappingData
  * ---
  */
 #define LOGICAL_REWRITE_FORMAT "map-%x-%x-%X_%X-%x-%x"
-void		CheckPointLogicalRewriteHeap(void);
+extern void CheckPointLogicalRewriteHeap(void);
 
 #endif							/* REWRITE_HEAP_H */
diff --git a/src/include/port/win32_port.h b/src/include/port/win32_port.h
index 5045ced91b..dbbf88f8e8 100644
--- a/src/include/port/win32_port.h
+++ b/src/include/port/win32_port.h
@@ -455,10 +455,10 @@ extern PGDLLIMPORT HANDLE pgwin32_initial_signal_pipe;
 #define UNBLOCKED_SIGNAL_QUEUE()	(pg_signal_queue & ~pg_signal_mask)
 #define PG_SIGNAL_COUNT 32
 
-void		pgwin32_signal_initialize(void);
-HANDLE		pgwin32_create_signal_listener(pid_t pid);
-void		pgwin32_dispatch_queued_signals(void);
-void		pg_queue_signal(int signum);
+extern void pgwin32_signal_initialize(void);
+extern HANDLE pgwin32_create_signal_listener(pid_t pid);
+extern void pgwin32_dispatch_queued_signals(void);
+extern void pg_queue_signal(int signum);
 
 /* In src/port/kill.c */
 #define kill(pid,sig)	pgkill(pid,sig)
@@ -475,15 +475,15 @@ extern int	pgkill(int pid, int sig);
 #define recv(s, buf, len, flags) pgwin32_recv(s, buf, len, flags)
 #define send(s, buf, len, flags) pgwin32_send(s, buf, len, flags)
 
-SOCKET		pgwin32_socket(int af, int type, int protocol);
-int			pgwin32_bind(SOCKET s, struct sockaddr *addr, int addrlen);
-int			pgwin32_listen(SOCKET s, int backlog);
-SOCKET		pgwin32_accept(SOCKET s, struct sockaddr *addr, int *addrlen);
-int			pgwin32_connect(SOCKET s, const struct sockaddr *name, int namelen);
-int			pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timeval *timeout);
-int			pgwin32_recv(SOCKET s, char *buf, int len, int flags);
-int			pgwin32_send(SOCKET s, const void *buf, int len, int flags);
-int			pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout);
+extern SOCKET pgwin32_socket(int af, int type, int protocol);
+extern int	pgwin32_bind(SOCKET s, struct sockaddr *addr, int addrlen);
+extern int	pgwin32_listen(SOCKET s, int backlog);
+extern SOCKET pgwin32_accept(SOCKET s, struct sockaddr *addr, int *addrlen);
+extern int	pgwin32_connect(SOCKET s, const struct sockaddr *name, int namelen);
+extern int	pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timeval *timeout);
+extern int	pgwin32_recv(SOCKET s, char *buf, int len, int flags);
+extern int	pgwin32_send(SOCKET s, const void *buf, int len, int flags);
+extern int	pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout);
 
 extern PGDLLIMPORT int pgwin32_noblock;
 
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
index b9686c2855..0b396c5669 100644
--- a/src/include/replication/message.h
+++ b/src/include/replication/message.h
@@ -34,8 +34,8 @@ extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
 
 /* RMGR API */
 #define XLOG_LOGICAL_MESSAGE	0x00
-void		logicalmsg_redo(XLogReaderState *record);
-void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
-const char *logicalmsg_identify(uint8 info);
+extern void logicalmsg_redo(XLogReaderState *record);
+extern void logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+extern const char *logicalmsg_identify(uint8 info);
 
 #endif							/* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/origin.h b/src/include/replication/origin.h
index 14d5c497ce..2d1b5e5c28 100644
--- a/src/include/replication/origin.h
+++ b/src/include/replication/origin.h
@@ -62,9 +62,9 @@ extern void CheckPointReplicationOrigin(void);
 extern void StartupReplicationOrigin(void);
 
 /* WAL logging */
-void		replorigin_redo(XLogReaderState *record);
-void		replorigin_desc(StringInfo buf, XLogReaderState *record);
-const char *replorigin_identify(uint8 info);
+extern void replorigin_redo(XLogReaderState *record);
+extern void replorigin_desc(StringInfo buf, XLogReaderState *record);
+extern const char *replorigin_identify(uint8 info);
 
 /* shared memory allocation */
 extern Size ReplicationOriginShmemSize(void);
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index f12e75d69b..4a01f877e5 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -618,68 +618,68 @@ struct ReorderBuffer
 };
 
 
-ReorderBuffer *ReorderBufferAllocate(void);
-void		ReorderBufferFree(ReorderBuffer *);
+extern ReorderBuffer *ReorderBufferAllocate(void);
+extern void ReorderBufferFree(ReorderBuffer *);
 
-ReorderBufferTupleBuf *ReorderBufferGetTupleBuf(ReorderBuffer *, Size tuple_len);
-void		ReorderBufferReturnTupleBuf(ReorderBuffer *, ReorderBufferTupleBuf *tuple);
-ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
-void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *, bool);
+extern ReorderBufferTupleBuf *ReorderBufferGetTupleBuf(ReorderBuffer *, Size tuple_len);
+extern void ReorderBufferReturnTupleBuf(ReorderBuffer *, ReorderBufferTupleBuf *tuple);
+extern ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
+extern void ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *, bool);
 
-Oid		   *ReorderBufferGetRelids(ReorderBuffer *, int nrelids);
-void		ReorderBufferReturnRelids(ReorderBuffer *, Oid *relids);
+extern Oid *ReorderBufferGetRelids(ReorderBuffer *, int nrelids);
+extern void ReorderBufferReturnRelids(ReorderBuffer *, Oid *relids);
 
-void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId,
+extern void ReorderBufferQueueChange(ReorderBuffer *, TransactionId,
 									 XLogRecPtr lsn, ReorderBufferChange *,
 									 bool toast_insert);
-void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, Snapshot snapshot, XLogRecPtr lsn,
+extern void ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, Snapshot snapshot, XLogRecPtr lsn,
 									  bool transactional, const char *prefix,
 									  Size message_size, const char *message);
-void		ReorderBufferCommit(ReorderBuffer *, TransactionId,
+extern void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 								XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 								TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
-void		ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
+extern void ReorderBufferFinishPrepared(ReorderBuffer *rb, TransactionId xid,
 										XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 										XLogRecPtr two_phase_at,
 										TimestampTz commit_time,
 										RepOriginId origin_id, XLogRecPtr origin_lsn,
 										char *gid, bool is_commit);
-void		ReorderBufferAssignChild(ReorderBuffer *, TransactionId, TransactionId, XLogRecPtr commit_lsn);
-void		ReorderBufferCommitChild(ReorderBuffer *, TransactionId, TransactionId,
+extern void ReorderBufferAssignChild(ReorderBuffer *, TransactionId, TransactionId, XLogRecPtr commit_lsn);
+extern void ReorderBufferCommitChild(ReorderBuffer *, TransactionId, TransactionId,
 									 XLogRecPtr commit_lsn, XLogRecPtr end_lsn);
-void		ReorderBufferAbort(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
-void		ReorderBufferAbortOld(ReorderBuffer *, TransactionId xid);
-void		ReorderBufferForget(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
-void		ReorderBufferInvalidate(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
+extern void ReorderBufferAbort(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
+extern void ReorderBufferAbortOld(ReorderBuffer *, TransactionId xid);
+extern void ReorderBufferForget(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
+extern void ReorderBufferInvalidate(ReorderBuffer *, TransactionId, XLogRecPtr lsn);
 
-void		ReorderBufferSetBaseSnapshot(ReorderBuffer *, TransactionId, XLogRecPtr lsn, struct SnapshotData *snap);
-void		ReorderBufferAddSnapshot(ReorderBuffer *, TransactionId, XLogRecPtr lsn, struct SnapshotData *snap);
-void		ReorderBufferAddNewCommandId(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+extern void ReorderBufferSetBaseSnapshot(ReorderBuffer *, TransactionId, XLogRecPtr lsn, struct SnapshotData *snap);
+extern void ReorderBufferAddSnapshot(ReorderBuffer *, TransactionId, XLogRecPtr lsn, struct SnapshotData *snap);
+extern void ReorderBufferAddNewCommandId(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
 										 CommandId cid);
-void		ReorderBufferAddNewTupleCids(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+extern void ReorderBufferAddNewTupleCids(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
 										 RelFileNode node, ItemPointerData pt,
 										 CommandId cmin, CommandId cmax, CommandId combocid);
-void		ReorderBufferAddInvalidations(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+extern void ReorderBufferAddInvalidations(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
 										  Size nmsgs, SharedInvalidationMessage *msgs);
-void		ReorderBufferImmediateInvalidation(ReorderBuffer *, uint32 ninvalidations,
+extern void ReorderBufferImmediateInvalidation(ReorderBuffer *, uint32 ninvalidations,
 											   SharedInvalidationMessage *invalidations);
-void		ReorderBufferProcessXid(ReorderBuffer *, TransactionId xid, XLogRecPtr lsn);
+extern void ReorderBufferProcessXid(ReorderBuffer *, TransactionId xid, XLogRecPtr lsn);
 
-void		ReorderBufferXidSetCatalogChanges(ReorderBuffer *, TransactionId xid, XLogRecPtr lsn);
-bool		ReorderBufferXidHasCatalogChanges(ReorderBuffer *, TransactionId xid);
-bool		ReorderBufferXidHasBaseSnapshot(ReorderBuffer *, TransactionId xid);
+extern void ReorderBufferXidSetCatalogChanges(ReorderBuffer *, TransactionId xid, XLogRecPtr lsn);
+extern bool ReorderBufferXidHasCatalogChanges(ReorderBuffer *, TransactionId xid);
+extern bool ReorderBufferXidHasBaseSnapshot(ReorderBuffer *, TransactionId xid);
 
-bool		ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
+extern bool ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
 											 XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
 											 TimestampTz prepare_time,
 											 RepOriginId origin_id, XLogRecPtr origin_lsn);
-void		ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid);
-void		ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid, char *gid);
-ReorderBufferTXN *ReorderBufferGetOldestTXN(ReorderBuffer *);
-TransactionId ReorderBufferGetOldestXmin(ReorderBuffer *rb);
+extern void ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid);
+extern void ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid, char *gid);
+extern ReorderBufferTXN *ReorderBufferGetOldestTXN(ReorderBuffer *);
+extern TransactionId ReorderBufferGetOldestXmin(ReorderBuffer *rb);
 
-void		ReorderBufferSetRestartPoint(ReorderBuffer *, XLogRecPtr ptr);
+extern void ReorderBufferSetRestartPoint(ReorderBuffer *, XLogRecPtr ptr);
 
-void		StartupReorderBuffer(void);
+extern void StartupReorderBuffer(void);
 
 #endif
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 4485d4ebee..901845abc2 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -99,8 +99,8 @@ extern char *LogicalRepSyncTableStart(XLogRecPtr *origin_startpos);
 extern bool AllTablesyncsReady(void);
 extern void UpdateTwoPhaseState(Oid suboid, char new_state);
 
-void		process_syncing_tables(XLogRecPtr current_lsn);
-void		invalidate_syncing_table_states(Datum arg, int cacheid,
+extern void process_syncing_tables(XLogRecPtr current_lsn);
+extern void invalidate_syncing_table_states(Datum arg, int cacheid,
 											uint32 hashvalue);
 
 static inline bool
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index 39faa4d837..98b4d718d2 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -1082,7 +1082,7 @@ init_spin_delay(SpinDelayStatus *status,
 }
 
 #define init_local_spin_delay(status) init_spin_delay(status, __FILE__, __LINE__, PG_FUNCNAME_MACRO)
-void perform_spin_delay(SpinDelayStatus *status);
-void finish_spin_delay(SpinDelayStatus *status);
+extern void perform_spin_delay(SpinDelayStatus *status);
+extern void finish_spin_delay(SpinDelayStatus *status);
 
 #endif	 /* S_LOCK_H */
diff --git a/src/include/tsearch/dicts/regis.h b/src/include/tsearch/dicts/regis.h
index c72f2702ca..c7c3d9fb34 100644
--- a/src/include/tsearch/dicts/regis.h
+++ b/src/include/tsearch/dicts/regis.h
@@ -38,12 +38,12 @@ typedef struct Regis
 				unused:15;
 } Regis;
 
-bool		RS_isRegis(const char *str);
+extern bool RS_isRegis(const char *str);
 
-void		RS_compile(Regis *r, bool issuffix, const char *str);
-void		RS_free(Regis *r);
+extern void RS_compile(Regis *r, bool issuffix, const char *str);
+extern void RS_free(Regis *r);
 
 /*returns true if matches */
-bool		RS_execute(Regis *r, char *str);
+extern bool RS_execute(Regis *r, char *str);
 
 #endif
diff --git a/src/include/utils/attoptcache.h b/src/include/utils/attoptcache.h
index cee6f5f18b..ee37af9500 100644
--- a/src/include/utils/attoptcache.h
+++ b/src/include/utils/attoptcache.h
@@ -23,6 +23,6 @@ typedef struct AttributeOpts
 	float8		n_distinct_inherited;
 } AttributeOpts;
 
-AttributeOpts *get_attribute_options(Oid spcid, int attnum);
+extern AttributeOpts *get_attribute_options(Oid spcid, int attnum);
 
 #endif							/* ATTOPTCACHE_H */
diff --git a/src/include/utils/numeric.h b/src/include/utils/numeric.h
index 21cd5a5cbf..3caa74dfe7 100644
--- a/src/include/utils/numeric.h
+++ b/src/include/utils/numeric.h
@@ -68,7 +68,7 @@ typedef struct NumericData *Numeric;
  */
 extern bool numeric_is_nan(Numeric num);
 extern bool numeric_is_inf(Numeric num);
-int32		numeric_maximum_size(int32 typmod);
+extern int32 numeric_maximum_size(int32 typmod);
 extern char *numeric_out_sci(Numeric num, int scale);
 extern char *numeric_normalize(Numeric num);
 
diff --git a/src/include/utils/pgstat_internal.h b/src/include/utils/pgstat_internal.h
index 0ee60b2f2a..0eccaea6c1 100644
--- a/src/include/utils/pgstat_internal.h
+++ b/src/include/utils/pgstat_internal.h
@@ -488,7 +488,7 @@ static inline void *pgstat_get_entry_data(PgStat_Kind kind, PgStatShared_Common
  * Functions in pgstat.c
  */
 
-const PgStat_KindInfo *pgstat_get_kind_info(PgStat_Kind kind);
+extern const PgStat_KindInfo *pgstat_get_kind_info(PgStat_Kind kind);
 
 #ifdef USE_ASSERT_CHECKING
 extern void pgstat_assert_is_up(void);
diff --git a/src/include/utils/spccache.h b/src/include/utils/spccache.h
index 68cc0aed7c..5163eeedbd 100644
--- a/src/include/utils/spccache.h
+++ b/src/include/utils/spccache.h
@@ -13,9 +13,9 @@
 #ifndef SPCCACHE_H
 #define SPCCACHE_H
 
-void		get_tablespace_page_costs(Oid spcid, float8 *spc_random_page_cost,
+extern void get_tablespace_page_costs(Oid spcid, float8 *spc_random_page_cost,
 									  float8 *spc_seq_page_cost);
-int			get_tablespace_io_concurrency(Oid spcid);
-int			get_tablespace_maintenance_io_concurrency(Oid spcid);
+extern int	get_tablespace_io_concurrency(Oid spcid);
+extern int	get_tablespace_maintenance_io_concurrency(Oid spcid);
 
 #endif							/* SPCCACHE_H */