diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index 7407672c9d..5736d03083 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -904,8 +904,7 @@ WaitForLockersMultiple(List *locktags, LOCKMODE lockmode, bool progress)
 
 	/*
 	 * Note: GetLockConflicts() never reports our own xid, hence we need not
-	 * check for that.  Also, prepared xacts are not reported, which is fine
-	 * since they certainly aren't going to do anything anymore.
+	 * check for that.  Also, prepared xacts are reported and awaited.
 	 */
 
 	/* Finally wait for each such transaction to complete */
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 20e50247ea..79c1cf9b8b 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -2903,9 +2903,7 @@ FastPathGetRelationLockEntry(LOCALLOCK *locallock)
  * so use of this function has to be thought about carefully.
  *
  * Note we never include the current xact's vxid in the result array,
- * since an xact never blocks itself.  Also, prepared transactions are
- * ignored, which is a bit more debatable but is appropriate for current
- * uses of the result.
+ * since an xact never blocks itself.
  */
 VirtualTransactionId *
 GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
@@ -2930,19 +2928,21 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 
 	/*
 	 * Allocate memory to store results, and fill with InvalidVXID.  We only
-	 * need enough space for MaxBackends + a terminator, since prepared xacts
-	 * don't count. InHotStandby allocate once in TopMemoryContext.
+	 * need enough space for MaxBackends + max_prepared_xacts + a terminator.
+	 * InHotStandby allocate once in TopMemoryContext.
 	 */
 	if (InHotStandby)
 	{
 		if (vxids == NULL)
 			vxids = (VirtualTransactionId *)
 				MemoryContextAlloc(TopMemoryContext,
-								   sizeof(VirtualTransactionId) * (MaxBackends + 1));
+								   sizeof(VirtualTransactionId) *
+								   (MaxBackends + max_prepared_xacts + 1));
 	}
 	else
 		vxids = (VirtualTransactionId *)
-			palloc0(sizeof(VirtualTransactionId) * (MaxBackends + 1));
+			palloc0(sizeof(VirtualTransactionId) *
+					(MaxBackends + max_prepared_xacts + 1));
 
 	/* Compute hash code and partition lock, and look up conflicting modes. */
 	hashcode = LockTagHashCode(locktag);
@@ -3017,13 +3017,9 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 				/* Conflict! */
 				GET_VXID_FROM_PGPROC(vxid, *proc);
 
-				/*
-				 * If we see an invalid VXID, then either the xact has already
-				 * committed (or aborted), or it's a prepared xact.  In either
-				 * case we may ignore it.
-				 */
 				if (VirtualTransactionIdIsValid(vxid))
 					vxids[count++] = vxid;
+				/* else, xact already committed or aborted */
 
 				/* No need to examine remaining slots. */
 				break;
@@ -3082,11 +3078,6 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 
 				GET_VXID_FROM_PGPROC(vxid, *proc);
 
-				/*
-				 * If we see an invalid VXID, then either the xact has already
-				 * committed (or aborted), or it's a prepared xact.  In either
-				 * case we may ignore it.
-				 */
 				if (VirtualTransactionIdIsValid(vxid))
 				{
 					int			i;
@@ -3098,6 +3089,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 					if (i >= fast_count)
 						vxids[count++] = vxid;
 				}
+				/* else, xact already committed or aborted */
 			}
 		}
 
@@ -3107,7 +3099,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
 
 	LWLockRelease(partitionLock);
 
-	if (count > MaxBackends)	/* should never happen */
+	if (count > MaxBackends + max_prepared_xacts)	/* should never happen */
 		elog(PANIC, "too many conflicting locks found");
 
 	vxids[count].backendId = InvalidBackendId;
@@ -4464,6 +4456,21 @@ VirtualXactLock(VirtualTransactionId vxid, bool wait)
 
 	Assert(VirtualTransactionIdIsValid(vxid));
 
+	if (VirtualTransactionIdIsPreparedXact(vxid))
+	{
+		LockAcquireResult lar;
+
+		/*
+		 * Prepared transactions don't hold vxid locks.  The
+		 * LocalTransactionId is always a normal, locked XID.
+		 */
+		SET_LOCKTAG_TRANSACTION(tag, vxid.localTransactionId);
+		lar = LockAcquire(&tag, ShareLock, false, !wait);
+		if (lar != LOCKACQUIRE_NOT_AVAIL)
+			LockRelease(&tag, ShareLock, false);
+		return lar != LOCKACQUIRE_NOT_AVAIL;
+	}
+
 	SET_LOCKTAG_VIRTUALTRANSACTION(tag, vxid);
 
 	/*
diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index 2e6ef174e9..68a3487d49 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -46,10 +46,10 @@ extern bool Debug_deadlocks;
 
 /*
  * Top-level transactions are identified by VirtualTransactionIDs comprising
- * the BackendId of the backend running the xact, plus a locally-assigned
- * LocalTransactionId.  These are guaranteed unique over the short term,
- * but will be reused after a database restart; hence they should never
- * be stored on disk.
+ * PGPROC fields backendId and lxid.  For prepared transactions, the
+ * LocalTransactionId is an ordinary XID.  These are guaranteed unique over
+ * the short term, but will be reused after a database restart or XID
+ * wraparound; hence they should never be stored on disk.
  *
  * Note that struct VirtualTransactionId can not be assumed to be atomically
  * assignable as a whole.  However, type LocalTransactionId is assumed to
@@ -61,15 +61,16 @@ extern bool Debug_deadlocks;
  */
 typedef struct
 {
-	BackendId	backendId;		/* determined at backend startup */
-	LocalTransactionId localTransactionId;	/* backend-local transaction id */
+	BackendId	backendId;		/* backendId from PGPROC */
+	LocalTransactionId localTransactionId;	/* lxid from PGPROC */
 } VirtualTransactionId;
 
 #define InvalidLocalTransactionId		0
 #define LocalTransactionIdIsValid(lxid) ((lxid) != InvalidLocalTransactionId)
 #define VirtualTransactionIdIsValid(vxid) \
-	(((vxid).backendId != InvalidBackendId) && \
-	 LocalTransactionIdIsValid((vxid).localTransactionId))
+	(LocalTransactionIdIsValid((vxid).localTransactionId))
+#define VirtualTransactionIdIsPreparedXact(vxid) \
+	((vxid).backendId == InvalidBackendId)
 #define VirtualTransactionIdEquals(vxid1, vxid2) \
 	((vxid1).backendId == (vxid2).backendId && \
 	 (vxid1).localTransactionId == (vxid2).localTransactionId)
diff --git a/src/test/isolation/Makefile b/src/test/isolation/Makefile
index d23e2cec64..edff04f041 100644
--- a/src/test/isolation/Makefile
+++ b/src/test/isolation/Makefile
@@ -62,12 +62,11 @@ installcheck: all
 check: all
 	$(pg_isolation_regress_check) --schedule=$(srcdir)/isolation_schedule
 
-# Versions of the check tests that include the prepared-transactions test
-# It only makes sense to run these if set up to use prepared transactions,
-# via TEMP_CONFIG for the check case, or via the postgresql.conf for the
-# installcheck case.
+# Non-default tests.  It only makes sense to run these if set up to use
+# prepared transactions, via TEMP_CONFIG for the check case, or via the
+# postgresql.conf for the installcheck case.
 installcheck-prepared-txns: all temp-install
-	$(pg_isolation_regress_installcheck) --schedule=$(srcdir)/isolation_schedule prepared-transactions
+	$(pg_isolation_regress_installcheck) --schedule=$(srcdir)/isolation_schedule prepared-transactions prepared-transactions-cic
 
 check-prepared-txns: all temp-install
-	$(pg_isolation_regress_check) --schedule=$(srcdir)/isolation_schedule prepared-transactions
+	$(pg_isolation_regress_check) --schedule=$(srcdir)/isolation_schedule prepared-transactions prepared-transactions-cic
diff --git a/src/test/isolation/README b/src/test/isolation/README
index 217953d183..6ae7152325 100644
--- a/src/test/isolation/README
+++ b/src/test/isolation/README
@@ -23,9 +23,9 @@ you can do something like
     ./pg_isolation_regress fk-contention fk-deadlock
 (look into the specs/ subdirectory to see the available tests).
 
-The prepared-transactions test requires the server's
-max_prepared_transactions parameter to be set to at least 3; therefore it
-is not run by default.  To include it in the test run, use
+Certain tests require the server's max_prepared_transactions parameter to be
+set to at least 3; therefore they are not run by default.  To include them in
+the test run, use
     make check-prepared-txns
 or
     make installcheck-prepared-txns
diff --git a/src/test/isolation/expected/prepared-transactions-cic.out b/src/test/isolation/expected/prepared-transactions-cic.out
new file mode 100644
index 0000000000..043ec3c363
--- /dev/null
+++ b/src/test/isolation/expected/prepared-transactions-cic.out
@@ -0,0 +1,18 @@
+Parsed test spec with 2 sessions
+
+starting permutation: w1 p1 cic2 c1 r2
+step w1: BEGIN; INSERT INTO cic_test VALUES (1);
+step p1: PREPARE TRANSACTION 's1';
+step cic2: 
+    CREATE INDEX CONCURRENTLY on cic_test(a);
+
+ERROR:  canceling statement due to lock timeout
+step c1: COMMIT PREPARED 's1';
+step r2: 
+    SET enable_seqscan to off;
+    SET enable_bitmapscan to off;
+    SELECT * FROM cic_test WHERE a = 1;
+
+a              
+
+1              
diff --git a/src/test/isolation/specs/prepared-transactions-cic.spec b/src/test/isolation/specs/prepared-transactions-cic.spec
new file mode 100644
index 0000000000..c39eaf5ad0
--- /dev/null
+++ b/src/test/isolation/specs/prepared-transactions-cic.spec
@@ -0,0 +1,37 @@
+# This test verifies that CREATE INDEX CONCURRENTLY interacts with prepared
+# transactions correctly.
+setup
+{
+    CREATE TABLE cic_test (a int);
+}
+
+teardown
+{
+    DROP TABLE cic_test;
+}
+
+
+# Sessions for CREATE INDEX CONCURRENTLY test
+session "s1"
+step "w1" { BEGIN; INSERT INTO cic_test VALUES (1); }
+step "p1" { PREPARE TRANSACTION 's1'; }
+step "c1" { COMMIT PREPARED 's1'; }
+
+session "s2"
+# The isolation tester never recognizes that a lock of s1 blocks s2, because a
+# prepared transaction's locks have no pid associated.  While there's a slight
+# chance of timeout while waiting for an autovacuum-held lock, that wouldn't
+# change the output.  Hence, no timeout is too short.
+setup { SET lock_timeout = 10; }
+step "cic2"
+{
+    CREATE INDEX CONCURRENTLY on cic_test(a);
+}
+step "r2"
+{
+    SET enable_seqscan to off;
+    SET enable_bitmapscan to off;
+    SELECT * FROM cic_test WHERE a = 1;
+}
+
+permutation  "w1" "p1" "cic2" "c1" "r2"