diff --git a/libraries/AP_Terrain/AP_Terrain.cpp b/libraries/AP_Terrain/AP_Terrain.cpp
index 89d96ce047..2c50a825eb 100644
--- a/libraries/AP_Terrain/AP_Terrain.cpp
+++ b/libraries/AP_Terrain/AP_Terrain.cpp
@@ -348,6 +348,13 @@ void AP_Terrain::update(void)
     // check for pending rally data
     update_rally_data();
 
+    // update tiles surrounding our current location:
+    if (pos_valid) {
+        have_surrounding_tiles = update_surrounding_tiles(loc);
+    } else {
+        have_surrounding_tiles = false;
+    }
+
     // update capabilities and status
     if (allocate()) {
         if (!pos_valid) {
@@ -362,7 +369,24 @@ void AP_Terrain::update(void)
     } else {
         system_status = TerrainStatusDisabled;
     }
+}
 
+bool AP_Terrain::update_surrounding_tiles(const Location &loc)
+{
+    // also request a larger set of up to 9 grids
+    bool ret = true;
+    for (int8_t x=-1; x<=1; x++) {
+        for (int8_t y=-1; y<=1; y++) {
+            Location loc2 = loc;
+            loc2.offset(x*TERRAIN_GRID_BLOCK_SIZE_X*0.7f*grid_spacing,
+                        y*TERRAIN_GRID_BLOCK_SIZE_Y*0.7f*grid_spacing);
+            float height;
+            if (!height_amsl(loc2, height)) {
+                ret = false;
+            }
+        }
+    }
+    return ret;
 }
 
 bool AP_Terrain::pre_arm_checks(char *failure_msg, uint8_t failure_msg_len) const
diff --git a/libraries/AP_Terrain/AP_Terrain.h b/libraries/AP_Terrain/AP_Terrain.h
index 7ae415d103..2ef374a94a 100644
--- a/libraries/AP_Terrain/AP_Terrain.h
+++ b/libraries/AP_Terrain/AP_Terrain.h
@@ -342,6 +342,9 @@ private:
     void write_block(void);
     void read_block(void);
 
+    // check for missing data in squares surrounding loc:
+    bool update_surrounding_tiles(const Location &loc);
+
     /*
       check for missing mission terrain data
      */
@@ -426,6 +429,10 @@ private:
     bool have_current_loc_height;
     float last_current_loc_height;
 
+    // true if we have all of the data for the squares around the
+    // current location:
+    bool have_surrounding_tiles;
+
     // next mission command to check
     uint16_t next_mission_index;
 
diff --git a/libraries/AP_Terrain/TerrainGCS.cpp b/libraries/AP_Terrain/TerrainGCS.cpp
index 4eed5931ab..340b2a7a5b 100644
--- a/libraries/AP_Terrain/TerrainGCS.cpp
+++ b/libraries/AP_Terrain/TerrainGCS.cpp
@@ -139,21 +139,10 @@ void AP_Terrain::send_request(mavlink_channel_t chan)
         return;
     }
 
-    // also request a larger set of up to 9 grids
-    for (int8_t x=-1; x<=1; x++) {
-        for (int8_t y=-1; y<=1; y++) {
-            Location loc2 = loc;
-            loc2.offset(x*TERRAIN_GRID_BLOCK_SIZE_X*0.7f*grid_spacing,
-                        y*TERRAIN_GRID_BLOCK_SIZE_Y*0.7f*grid_spacing);
-            struct grid_info info2;
-            calculate_grid_info(loc2, info2);            
-            if (request_missing(chan, info2)) {
-                return;
-            }
-        }
-    }
-
-    // check cache blocks that may have been setup by a TERRAIN_CHECK
+    // check cache blocks that may have been setup by a TERRAIN_CHECK,
+    // mission items, rally items, squares surrounding our current
+    // location, favourite holiday destination, scripting, height
+    // reference location, ....
     if (send_cache_request(chan)) {
         return;
     }