diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c
index ce9ede4c196..4b4f1e1965b 100644
--- a/src/backend/utils/mmgr/dsa.c
+++ b/src/backend/utils/mmgr/dsa.c
@@ -2196,6 +2196,8 @@ make_new_segment(dsa_area *area, size_t requested_pages)
 	/* See if that is enough... */
 	if (requested_pages > usable_pages)
 	{
+		size_t		total_requested_pages PG_USED_FOR_ASSERTS_ONLY;
+
 		/*
 		 * We'll make an odd-sized segment, working forward from the requested
 		 * number of pages.
@@ -2206,10 +2208,37 @@ make_new_segment(dsa_area *area, size_t requested_pages)
 			MAXALIGN(sizeof(FreePageManager)) +
 			usable_pages * sizeof(dsa_pointer);
 
+		/*
+		 * We must also account for pagemap entries needed to cover the
+		 * metadata pages themselves.  The pagemap must track all pages in the
+		 * segment, including the pages occupied by metadata.
+		 *
+		 * This formula uses integer ceiling division to compute the exact
+		 * number of additional entries needed.  The divisor (FPM_PAGE_SIZE -
+		 * sizeof(dsa_pointer)) accounts for the fact that each metadata page
+		 * consumes one pagemap entry of sizeof(dsa_pointer) bytes, leaving
+		 * only (FPM_PAGE_SIZE - sizeof(dsa_pointer)) net bytes per metadata
+		 * page.
+		 */
+		metadata_bytes +=
+			((metadata_bytes + (FPM_PAGE_SIZE - sizeof(dsa_pointer)) - 1) /
+			 (FPM_PAGE_SIZE - sizeof(dsa_pointer))) *
+			sizeof(dsa_pointer);
+
 		/* Add padding up to next page boundary. */
 		if (metadata_bytes % FPM_PAGE_SIZE != 0)
 			metadata_bytes += FPM_PAGE_SIZE - (metadata_bytes % FPM_PAGE_SIZE);
 		total_size = metadata_bytes + usable_pages * FPM_PAGE_SIZE;
+		total_requested_pages = total_size / FPM_PAGE_SIZE;
+
+		/*
+		 * Verify that we allocated enough pagemap entries for metadata and
+		 * usable pages.  This reverse-engineers the new calculation of
+		 * "metadata_bytes" done based on the new "requested_pages" for an
+		 * odd-sized segment.
+		 */
+		Assert((metadata_bytes - MAXALIGN(sizeof(dsa_segment_header)) -
+				MAXALIGN(sizeof(FreePageManager))) / sizeof(dsa_pointer) >= total_requested_pages);
 
 		/* Is that too large for dsa_pointer's addressing scheme? */
 		if (total_size > DSA_MAX_SEGMENT_SIZE)
diff --git a/src/test/modules/test_dsa/expected/test_dsa.out b/src/test/modules/test_dsa/expected/test_dsa.out
index 266010e77fe..4b53a7de4a4 100644
--- a/src/test/modules/test_dsa/expected/test_dsa.out
+++ b/src/test/modules/test_dsa/expected/test_dsa.out
@@ -11,3 +11,19 @@ SELECT test_dsa_resowners();
  
 (1 row)
 
+-- Test allocations across a pre-defined range of pages.  This covers enough
+-- range to check for the case of odd-sized segments, without making the test
+-- too slow.
+SELECT test_dsa_allocate(1001, 2000, 100);
+ test_dsa_allocate 
+-------------------
+ 
+(1 row)
+
+-- Larger size with odd-sized segment.
+SELECT test_dsa_allocate(6501, 6600, 100);
+ test_dsa_allocate 
+-------------------
+ 
+(1 row)
+
diff --git a/src/test/modules/test_dsa/sql/test_dsa.sql b/src/test/modules/test_dsa/sql/test_dsa.sql
index c3d8db94372..99b4a60dd14 100644
--- a/src/test/modules/test_dsa/sql/test_dsa.sql
+++ b/src/test/modules/test_dsa/sql/test_dsa.sql
@@ -2,3 +2,10 @@ CREATE EXTENSION test_dsa;
 
 SELECT test_dsa_basic();
 SELECT test_dsa_resowners();
+
+-- Test allocations across a pre-defined range of pages.  This covers enough
+-- range to check for the case of odd-sized segments, without making the test
+-- too slow.
+SELECT test_dsa_allocate(1001, 2000, 100);
+-- Larger size with odd-sized segment.
+SELECT test_dsa_allocate(6501, 6600, 100);
diff --git a/src/test/modules/test_dsa/test_dsa--1.0.sql b/src/test/modules/test_dsa/test_dsa--1.0.sql
index 2904cb23525..3ee2e44cc00 100644
--- a/src/test/modules/test_dsa/test_dsa--1.0.sql
+++ b/src/test/modules/test_dsa/test_dsa--1.0.sql
@@ -10,3 +10,7 @@ CREATE FUNCTION test_dsa_basic()
 CREATE FUNCTION test_dsa_resowners()
 	RETURNS pg_catalog.void
 	AS 'MODULE_PATHNAME' LANGUAGE C;
+
+CREATE FUNCTION test_dsa_allocate(int, int, int)
+	RETURNS pg_catalog.void
+	AS 'MODULE_PATHNAME' LANGUAGE C;
diff --git a/src/test/modules/test_dsa/test_dsa.c b/src/test/modules/test_dsa/test_dsa.c
index ed2a07c962f..edcab105de6 100644
--- a/src/test/modules/test_dsa/test_dsa.c
+++ b/src/test/modules/test_dsa/test_dsa.c
@@ -16,6 +16,7 @@
 #include "storage/dsm_registry.h"
 #include "storage/lwlock.h"
 #include "utils/dsa.h"
+#include "utils/freepage.h"
 #include "utils/resowner.h"
 
 PG_MODULE_MAGIC;
@@ -120,3 +121,42 @@ test_dsa_resowners(PG_FUNCTION_ARGS)
 
 	PG_RETURN_VOID();
 }
+
+/*
+ * test_dsa_allocate
+ *
+ * Test DSA allocation across a range of sizes to exercise the pagemap
+ * sizing logic in make_new_segment().  A fresh DSA is created for each
+ * iteration so that each allocation triggers a new segment creation,
+ * including the odd-sized segment path.
+ */
+PG_FUNCTION_INFO_V1(test_dsa_allocate);
+Datum
+test_dsa_allocate(PG_FUNCTION_ARGS)
+{
+	int			start_num_pages = PG_GETARG_INT32(0);
+	int			end_num_pages = PG_GETARG_INT32(1);
+	int			step = PG_GETARG_INT32(2);
+	size_t		usable_pages;
+	int		   *tranche_id;
+	bool		found;
+	dsa_area   *a;
+	dsa_pointer dp;
+
+	if (start_num_pages > end_num_pages)
+		elog(ERROR, "incorrect start and end parameters");
+
+	tranche_id = GetNamedDSMSegment("test_dsa", sizeof(int),
+									init_tranche, &found, NULL);
+
+	for (usable_pages = start_num_pages; usable_pages < end_num_pages; usable_pages += step)
+	{
+		a = dsa_create(*tranche_id);
+		dp = dsa_allocate(a, usable_pages * FPM_PAGE_SIZE);
+
+		dsa_free(a, dp);
+		dsa_detach(a);
+	}
+
+	PG_RETURN_VOID();
+}