diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -1382,6 +1382,7 @@ static inline int index_baserev(indexObj
 static int index_issnapshotrev(indexObject *self, Py_ssize_t rev)
 {
 	int ps[2];
+	int b;
 	Py_ssize_t base;
 	while (rev >= 0) {
 		base = (Py_ssize_t)index_baserev(self, rev);
@@ -1399,6 +1400,20 @@ static int index_issnapshotrev(indexObje
 			assert(PyErr_Occurred());
 			return -1;
 		};
+		while ((index_get_length(self, ps[0]) == 0) && ps[0] >= 0) {
+			b = index_baserev(self, ps[0]);
+			if (b == ps[0]) {
+				break;
+			}
+			ps[0] = b;
+		}
+		while ((index_get_length(self, ps[1]) == 0) && ps[1] >= 0) {
+			b = index_baserev(self, ps[1]);
+			if (b == ps[1]) {
+				break;
+			}
+			ps[1] = b;
+		}
 		if (base == ps[0] || base == ps[1]) {
 			return 0;
 		}
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1775,7 +1775,17 @@ class revlog:
         if base == nullrev:
             return True
         p1 = entry[5]
+        while self.length(p1) == 0:
+            b = self.deltaparent(p1)
+            if b == p1:
+                break
+            p1 = b
         p2 = entry[6]
+        while self.length(p2) == 0:
+            b = self.deltaparent(p2)
+            if b == p2:
+                break
+            p2 = b
         if base == p1 or base == p2:
             return False
         return self.issnapshot(base)