diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 02894a7e35..8cd5843885 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -927,7 +927,7 @@ build_tlist_to_deparse(RelOptInfo *foreignrel)
  *
  * List of columns selected is returned in retrieved_attrs.
  */
-extern void
+void
 deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
 						List *tlist, List *remote_conds, List *pathkeys,
 						bool is_subquery, List **retrieved_attrs,
@@ -1313,7 +1313,7 @@ appendConditions(List *exprs, deparse_expr_cxt *context)
 }
 
 /* Output join name for given join type */
-extern const char *
+const char *
 get_jointype_name(JoinType jointype)
 {
 	switch (jointype)
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index d37180ae10..941a2e75a5 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5567,7 +5567,7 @@ conversion_error_callback(void *arg)
  * Find an equivalence class member expression, all of whose Vars, come from
  * the indicated relation.
  */
-extern Expr *
+Expr *
 find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel)
 {
 	ListCell   *lc_em;
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index f2cb6d7fb8..5fa87f5757 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -4023,7 +4023,7 @@ ResetReindexPending(void)
  * EstimateReindexStateSpace
  *		Estimate space needed to pass reindex state to parallel workers.
  */
-extern Size
+Size
 EstimateReindexStateSpace(void)
 {
 	return offsetof(SerializedReindexState, pendingReindexedIndexes)
@@ -4034,7 +4034,7 @@ EstimateReindexStateSpace(void)
  * SerializeReindexState
  *		Serialize reindex state for parallel workers.
  */
-extern void
+void
 SerializeReindexState(Size maxsize, char *start_address)
 {
 	SerializedReindexState *sistate = (SerializedReindexState *) start_address;
@@ -4052,7 +4052,7 @@ SerializeReindexState(Size maxsize, char *start_address)
  * RestoreReindexState
  *		Restore reindex state in a parallel worker.
  */
-extern void
+void
 RestoreReindexState(void *reindexstate)
 {
 	SerializedReindexState *sistate = (SerializedReindexState *) reindexstate;
diff --git a/src/backend/catalog/partition.c b/src/backend/catalog/partition.c
index 4dddfcc014..b1c7cd6c72 100644
--- a/src/backend/catalog/partition.c
+++ b/src/backend/catalog/partition.c
@@ -856,7 +856,7 @@ partition_bounds_equal(int partnatts, int16 *parttyplen, bool *parttypbyval,
  * Return a copy of given PartitionBoundInfo structure. The data types of bounds
  * are described by given partition key specification.
  */
-extern PartitionBoundInfo
+PartitionBoundInfo
 partition_bounds_copy(PartitionBoundInfo src,
 					  PartitionKey key)
 {
diff --git a/src/backend/foreign/foreign.c b/src/backend/foreign/foreign.c
index e7fd507fa5..eac78a5d31 100644
--- a/src/backend/foreign/foreign.c
+++ b/src/backend/foreign/foreign.c
@@ -712,7 +712,7 @@ get_foreign_server_oid(const char *servername, bool missing_ok)
  * path list in RelOptInfo is anyway sorted by total cost we are likely to
  * choose the most efficient path, which is all for the best.
  */
-extern Path *
+Path *
 GetExistingLocalJoinPath(RelOptInfo *joinrel)
 {
 	ListCell   *lc;
diff --git a/src/backend/storage/ipc/shm_toc.c b/src/backend/storage/ipc/shm_toc.c
index 2abd140a96..ee5ec6e380 100644
--- a/src/backend/storage/ipc/shm_toc.c
+++ b/src/backend/storage/ipc/shm_toc.c
@@ -60,7 +60,7 @@ shm_toc_create(uint64 magic, void *address, Size nbytes)
  * Attach to an existing table of contents.  If the magic number found at
  * the target address doesn't match our expectations, return NULL.
  */
-extern shm_toc *
+shm_toc *
 shm_toc_attach(uint64 magic, void *address)
 {
 	shm_toc    *toc = (shm_toc *) address;
@@ -84,7 +84,7 @@ shm_toc_attach(uint64 magic, void *address)
  * We allocate backwards from the end of the segment, so that the TOC entries
  * can grow forward from the start of the segment.
  */
-extern void *
+void *
 shm_toc_allocate(shm_toc *toc, Size nbytes)
 {
 	volatile shm_toc *vtoc = toc;
@@ -127,7 +127,7 @@ shm_toc_allocate(shm_toc *toc, Size nbytes)
 /*
  * Return the number of bytes that can still be allocated.
  */
-extern Size
+Size
 shm_toc_freespace(shm_toc *toc)
 {
 	volatile shm_toc *vtoc = toc;
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 3ba9bb3519..6f0fe94d63 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -1843,7 +1843,7 @@ add_json(Datum val, bool is_null, StringInfo result,
 /*
  * SQL function array_to_json(row)
  */
-extern Datum
+Datum
 array_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
@@ -1859,7 +1859,7 @@ array_to_json(PG_FUNCTION_ARGS)
 /*
  * SQL function array_to_json(row, prettybool)
  */
-extern Datum
+Datum
 array_to_json_pretty(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
@@ -1876,7 +1876,7 @@ array_to_json_pretty(PG_FUNCTION_ARGS)
 /*
  * SQL function row_to_json(row)
  */
-extern Datum
+Datum
 row_to_json(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);
@@ -1892,7 +1892,7 @@ row_to_json(PG_FUNCTION_ARGS)
 /*
  * SQL function row_to_json(row, prettybool)
  */
-extern Datum
+Datum
 row_to_json_pretty(PG_FUNCTION_ARGS)
 {
 	Datum		array = PG_GETARG_DATUM(0);