diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index c90fe40b3c9b21073943b2b32117069052917e87..5d0fc77c3015a739e2270d16a704818aa3bbedc9 100644
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -500,7 +500,9 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
 	 * Both nbuckets and nbatch must be powers of 2 to make
 	 * ExecHashGetBucketAndBatch fast.	We already fixed nbatch; now inflate
 	 * nbuckets to the next larger power of 2.	We also force nbuckets to not
-	 * be real small, by starting the search at 2^10.
+	 * be real small, by starting the search at 2^10.  (Note: above we made
+	 * sure that nbuckets is not more than INT_MAX / 2, so this loop cannot
+	 * overflow, nor can the final shift to recalculate nbuckets.)
 	 */
 	i = 10;
 	while ((1 << i) < nbuckets)
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index 31ac2b25e8ffa2f50dfa4c9bde0d248baf2c0979..07f7a84943029f876abcd853c7b2b85bdd0e048a 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -68,6 +68,8 @@
 
 #include "postgres.h"
 
+#include <limits.h>
+
 #include "access/xact.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
@@ -205,6 +207,8 @@ static void hdefault(HTAB *hashp);
 static int	choose_nelem_alloc(Size entrysize);
 static bool init_htab(HTAB *hashp, long nelem);
 static void hash_corrupted(HTAB *hashp);
+static long next_pow2_long(long num);
+static int	next_pow2_int(long num);
 static void register_seq_scan(HTAB *hashp);
 static void deregister_seq_scan(HTAB *hashp);
 static bool has_seq_scans(HTAB *hashp);
@@ -379,8 +383,13 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
 	{
 		/* Doesn't make sense to partition a local hash table */
 		Assert(flags & HASH_SHARED_MEM);
-		/* # of partitions had better be a power of 2 */
-		Assert(info->num_partitions == (1L << my_log2(info->num_partitions)));
+
+		/*
+		 * The number of partitions had better be a power of 2. Also, it must
+		 * be less than INT_MAX (see init_htab()), so call the int version of
+		 * next_pow2.
+		 */
+		Assert(info->num_partitions == next_pow2_int(info->num_partitions));
 
 		hctl->num_partitions = info->num_partitions;
 	}
@@ -523,7 +532,6 @@ init_htab(HTAB *hashp, long nelem)
 {
 	HASHHDR    *hctl = hashp->hctl;
 	HASHSEGMENT *segp;
-	long		lnbuckets;
 	int			nbuckets;
 	int			nsegs;
 
@@ -538,9 +546,7 @@ init_htab(HTAB *hashp, long nelem)
 	 * number of buckets.  Allocate space for the next greater power of two
 	 * number of buckets
 	 */
-	lnbuckets = (nelem - 1) / hctl->ffactor + 1;
-
-	nbuckets = 1 << my_log2(lnbuckets);
+	nbuckets = next_pow2_int((nelem - 1) / hctl->ffactor + 1);
 
 	/*
 	 * In a partitioned table, nbuckets must be at least equal to
@@ -558,7 +564,7 @@ init_htab(HTAB *hashp, long nelem)
 	 * Figure number of directory segments needed, round up to a power of 2
 	 */
 	nsegs = (nbuckets - 1) / hctl->ssize + 1;
-	nsegs = 1 << my_log2(nsegs);
+	nsegs = next_pow2_int(nsegs);
 
 	/*
 	 * Make sure directory is big enough. If pre-allocated directory is too
@@ -628,9 +634,9 @@ hash_estimate_size(long num_entries, Size entrysize)
 				elementAllocCnt;
 
 	/* estimate number of buckets wanted */
-	nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
+	nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
 	/* # of segments needed for nBuckets */
-	nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
+	nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
 	/* directory entries */
 	nDirEntries = DEF_DIRSIZE;
 	while (nDirEntries < nSegments)
@@ -671,9 +677,9 @@ hash_select_dirsize(long num_entries)
 				nDirEntries;
 
 	/* estimate number of buckets wanted */
-	nBuckets = 1L << my_log2((num_entries - 1) / DEF_FFACTOR + 1);
+	nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
 	/* # of segments needed for nBuckets */
-	nSegments = 1L << my_log2((nBuckets - 1) / DEF_SEGSIZE + 1);
+	nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
 	/* directory entries */
 	nDirEntries = DEF_DIRSIZE;
 	while (nDirEntries < nSegments)
@@ -1408,11 +1414,32 @@ my_log2(long num)
 	int			i;
 	long		limit;
 
+	/* guard against too-large input, which would put us into infinite loop */
+	if (num > LONG_MAX / 2)
+		num = LONG_MAX / 2;
+
 	for (i = 0, limit = 1; limit < num; i++, limit <<= 1)
 		;
 	return i;
 }
 
+/* calculate first power of 2 >= num, bounded to what will fit in a long */
+static long
+next_pow2_long(long num)
+{
+	/* my_log2's internal range check is sufficient */
+	return 1L << my_log2(num);
+}
+
+/* calculate first power of 2 >= num, bounded to what will fit in an int */
+static int
+next_pow2_int(long num)
+{
+	if (num > INT_MAX / 2)
+		num = INT_MAX / 2;
+	return 1 << my_log2(num);
+}
+
 
 /************************* SEQ SCAN TRACKING ************************/