diff --git a/src/seen.c b/src/seen.c
index 2bbc529b0..1b147fb19 100644
--- a/src/seen.c
+++ b/src/seen.c
@@ -96,30 +96,45 @@ seen_region *find_seen(struct seen_region *seehash[], const region * r)
     return NULL;
 }
 
-void get_seen_interval(struct seen_region *seen[], struct region **firstp, struct region **lastp)
-{
-    /* this is required to find the neighbour regions of the ones we are in,
-     * which may well be outside of [firstregion, lastregion) */
+void seenhash_map(struct seen_region *seen[], void(*cb)(seen_region *, void *), void *cbdata) {
     int i;
-    region *first, *last;
-
-    assert(seen && firstp && lastp);
-    first = *firstp;
-    last = *lastp;
     for (i = 0; i != MAXSEEHASH; ++i) {
         seen_region *sr = seen[i];
         while (sr != NULL) {
-            if (first == NULL || sr->r->index < first->index) {
-                first = sr->r;
-            }
-            if (last != NULL && sr->r->index >= last->index) {
-                last = sr->r->next;
-            }
+            cb(sr, cbdata);
             sr = sr->nextHash;
         }
     }
-    *firstp = first;
-    *lastp = last;
+}
+
+typedef struct cb_interval {
+    region *first;
+    region *last;
+} cb_interval;
+
+static void cb_get_interval(seen_region *sr, void *cbdata) {
+    cb_interval *iv = (cb_interval *)cbdata;
+    region *r = sr->r;
+    if (iv->first == NULL || r->index < iv->first->index) {
+        iv->first = r;
+    }
+    if (iv->last != NULL && r->index >= iv->last->index) {
+        iv->last = r->next;
+    }
+}
+
+/* this function adds the neighbour regions of the ones we have seen
+ * to the interval, which may be outside of [faction.first, faction.last)
+ */
+void get_seen_interval(struct seen_region *seen[], struct region **firstp, struct region **lastp)
+{
+    cb_interval interval;
+
+    interval.first = *firstp;
+    interval.last = *lastp;
+    seenhash_map(seen, cb_get_interval, &interval);
+    *firstp = interval.first;
+    *lastp = interval.last;
 }
 
 bool add_seen(struct seen_region *seehash[], struct region *r, unsigned char mode, bool dis)
diff --git a/src/seen.h b/src/seen.h
index 9e6312d78..2a393adf2 100644
--- a/src/seen.h
+++ b/src/seen.h
@@ -53,6 +53,7 @@ struct seen_region *find_seen(struct seen_region *seehash[], const struct region
 void get_seen_interval(struct seen_region *seen[], struct region **firstp, struct region **lastp);
 bool add_seen(struct seen_region *seehash[], struct region *r, unsigned char mode, bool dis);
 void link_seen(struct seen_region *seehash[], const struct region *first, const struct region *last);
+void seenhash_map(struct seen_region *seen[], void(*cb)(struct seen_region *, void *), void *cbdata);
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/seen.test.c b/src/seen.test.c
index be2189c14..a181a690d 100644
--- a/src/seen.test.c
+++ b/src/seen.test.c
@@ -121,6 +121,28 @@ static void test_seen_interval_forward(CuTest *tc) {
     test_cleanup();
 }
 
+static void cb_testmap(seen_region *sr, void *cbdata) {
+    int *ip = (int *)cbdata;
+    *ip += sr->r->y;
+}
+
+static void test_seenhash_map(CuTest *tc) {
+    region *r;
+    seen_region **seen;
+    int i = 0;
+
+    test_cleanup();
+    seen = seen_init();
+    r = test_create_region(1, 1, 0);
+    add_seen(seen, r, see_unit, false);
+    r = test_create_region(2, 2, 0);
+    add_seen(seen, r, see_unit, false);
+    seenhash_map(seen, cb_testmap, &i);
+    CuAssertIntEquals(tc, 3, i);
+    seen_done(seen);
+    test_cleanup();
+}
+
 CuSuite *get_seen_suite(void)
 {
     CuSuite *suite = CuSuiteNew();
@@ -129,5 +151,6 @@ CuSuite *get_seen_suite(void)
     SUITE_ADD_TEST(suite, test_seen_region);
     SUITE_ADD_TEST(suite, test_seen_interval_backward);
     SUITE_ADD_TEST(suite, test_seen_interval_forward);
+    SUITE_ADD_TEST(suite, test_seenhash_map);
     return suite;
 }