diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 921f029..1070812 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -671,6 +671,7 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 	{
 		DWORD		size_high;
 		DWORD		size_low;
+		DWORD		errcode;
 
 		/* Shifts >= the width of the type are undefined. */
 #ifdef _WIN64
@@ -686,9 +687,21 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 								 size_high,		/* Upper 32 bits of size */
 								 size_low,		/* Lower 32 bits of size */
 								 name);
+
+		/*
+		 * If the mapping already exists, CreateFileMapping returns a valid
+		 * handle but sets ERROR_ALREADY_EXISTS. Return false for the case.
+		 * CreateFileMapping may return ERROR_ACCESS_DENIED for the cases when
+		 * running as a service. It also tells that the mapping is already
+		 * created by someone else, so return false.
+		 */
+		errcode = GetLastError();
+		if (errcode == ERROR_ALREADY_EXISTS || errcode == ERROR_ACCESS_DENIED)
+		  return false;
+
 		if (!hmap)
 		{
-			_dosmaperr(GetLastError());
+			_dosmaperr(errcode);
 			ereport(elevel,
 					(errcode_for_dynamic_shared_memory(),
 				  errmsg("could not create shared memory segment \"%s\": %m",