diff --git a/src/backend/port/posix_sema.c b/src/backend/port/posix_sema.c
index 269c7460817e..d7fb0c0c4da0 100644
--- a/src/backend/port/posix_sema.c
+++ b/src/backend/port/posix_sema.c
@@ -215,12 +215,8 @@ PGReserveSemaphores(int maxSemas)
 		elog(PANIC, "out of memory");
 #else
 
-	/*
-	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
-	 * ShmemAlloc() won't be ready yet.
-	 */
 	sharedSemas = (PGSemaphore)
-		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+		ShmemAlloc(PGSemaphoreShmemSize(maxSemas));
 #endif
 
 	numSems = 0;
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c
index 6ac83ea1a821..9faaeeefc790 100644
--- a/src/backend/port/sysv_sema.c
+++ b/src/backend/port/sysv_sema.c
@@ -343,12 +343,8 @@ PGReserveSemaphores(int maxSemas)
 				 errmsg("could not stat data directory \"%s\": %m",
 						DataDir)));
 
-	/*
-	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
-	 * ShmemAlloc() won't be ready yet.
-	 */
 	sharedSemas = (PGSemaphore)
-		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));
+		ShmemAlloc(PGSemaphoreShmemSize(maxSemas));
 	numSharedSemas = 0;
 	maxSharedSemas = maxSemas;
 
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 2fa045e6b0f6..81bbb7cefaf5 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -86,17 +86,9 @@ RequestAddinShmemSpace(Size size)
  * required.
  */
 Size
-CalculateShmemSize(int *num_semaphores)
+CalculateShmemSize(void)
 {
 	Size		size;
-	int			numSemas;
-
-	/* Compute number of semaphores we'll need */
-	numSemas = ProcGlobalSemas();
-
-	/* Return the number of semaphores if requested by the caller */
-	if (num_semaphores)
-		*num_semaphores = numSemas;
 
 	/*
 	 * Size of the Postgres shared-memory block is estimated via moderately-
@@ -108,7 +100,6 @@ CalculateShmemSize(int *num_semaphores)
 	 * during the actual allocation phase.
 	 */
 	size = 100000;
-	size = add_size(size, PGSemaphoreShmemSize(numSemas));
 	size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
@@ -202,12 +193,11 @@ CreateSharedMemoryAndSemaphores(void)
 	PGShmemHeader *shim;
 	PGShmemHeader *seghdr;
 	Size		size;
-	int			numSemas;
 
 	Assert(!IsUnderPostmaster);
 
 	/* Compute the size of the shared-memory block */
-	size = CalculateShmemSize(&numSemas);
+	size = CalculateShmemSize();
 	elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
 
 	/*
@@ -224,11 +214,6 @@ CreateSharedMemoryAndSemaphores(void)
 
 	InitShmemAccess(seghdr);
 
-	/*
-	 * Create semaphores
-	 */
-	PGReserveSemaphores(numSemas);
-
 	/*
 	 * Set up shared memory allocation mechanism
 	 */
@@ -358,12 +343,11 @@ InitializeShmemGUCs(void)
 	Size		size_b;
 	Size		size_mb;
 	Size		hp_size;
-	int			num_semas;
 
 	/*
 	 * Calculate the shared memory size and round up to the nearest megabyte.
 	 */
-	size_b = CalculateShmemSize(&num_semas);
+	size_b = CalculateShmemSize();
 	size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
 	sprintf(buf, "%zu", size_mb);
 	SetConfigOption("shared_memory_size", buf,
@@ -383,6 +367,6 @@ InitializeShmemGUCs(void)
 						PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 	}
 
-	sprintf(buf, "%d", num_semas);
+	sprintf(buf, "%d", ProcGlobalSemas());
 	SetConfigOption("num_os_semaphores", buf, PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 }
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 96f29aafc391..4a21c1bb6567 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -144,6 +144,7 @@ ProcGlobalShmemSize(void)
 	size = add_size(size, sizeof(PROC_HDR));
 	size = add_size(size, sizeof(slock_t));
 
+	size = add_size(size, PGSemaphoreShmemSize(ProcGlobalSemas()));
 	size = add_size(size, PGProcShmemSize());
 	size = add_size(size, FastPathLockShmemSize());
 
@@ -286,6 +287,9 @@ InitProcGlobal(void)
 	/* For asserts checking we did not overflow. */
 	fpEndPtr = fpPtr + requestSize;
 
+	/* Reserve space for semaphores. */
+	PGReserveSemaphores(ProcGlobalSemas());
+
 	for (i = 0; i < TotalProcs; i++)
 	{
 		PGPROC	   *proc = &procs[i];
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 3baf418b3d1e..2a8a8f0eabdb 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -77,7 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
 /* ipci.c */
 extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
 
-extern Size CalculateShmemSize(int *num_semaphores);
+extern Size CalculateShmemSize(void);
 extern void CreateSharedMemoryAndSemaphores(void);
 #ifdef EXEC_BACKEND
 extern void AttachSharedMemoryStructs(void);