diff --git a/rust/hg-core/src/ancestors.rs b/rust/hg-core/src/ancestors.rs
--- a/rust/hg-core/src/ancestors.rs
+++ b/rust/hg-core/src/ancestors.rs
@@ -345,14 +345,6 @@ impl<G: Graph> MissingAncestors<G> {
             if revs_visit.remove(&curr) {
                 missing.push(curr);
                 this_visit_is_revs = true;
-            } else if bases_visit.contains(&curr) {
-                this_visit_is_revs = false;
-            } else {
-                // not an ancestor of revs or bases: ignore
-                continue;
-            }
-
-            {
                 for p in self.graph.parents(curr)?.iter().cloned() {
                     if p == NULL_REVISION {
                         continue;
@@ -378,6 +370,35 @@ impl<G: Graph> MissingAncestors<G> {
                         }
                     }
                 }
+            } else if bases_visit.contains(&curr) {
+                this_visit_is_revs = false;
+                for p in self.graph.parents(curr)?.iter().cloned() {
+                    if p == NULL_REVISION {
+                        continue;
+                    }
+                    let in_other_visit = if this_visit_is_revs {
+                        bases_visit.contains(&p)
+                    } else {
+                        revs_visit.contains(&p)
+                    };
+                    if in_other_visit || both_visit.contains(&p) {
+                        // p is implicitely in this_visit.
+                        // This means p is or should be in bothvisit
+                        // TODO optim: hence if bothvisit, we look up twice
+                        revs_visit.remove(&p);
+                        bases_visit.insert(p);
+                        both_visit.insert(p);
+                    } else {
+                        // visit later
+                        if this_visit_is_revs {
+                            revs_visit.insert(p);
+                        } else {
+                            bases_visit.insert(p);
+                        }
+                    }
+                }
+            } else {
+                // not an ancestor of revs or bases: ignore
             }
         }
         missing.reverse();