diff --git a/sample-config/pgmon-metrics.yml b/sample-config/pgmon-metrics.yml
index e0aad5b..711e2a9 100644
--- a/sample-config/pgmon-metrics.yml
+++ b/sample-config/pgmon-metrics.yml
@@ -38,7 +38,7 @@ metrics:
   hit_ratios:
     type: row
     query:
-      0: SELECT sum(heap_blks_read)::float / sum(heap_blks_read + heap_blks_hit) AS avg_heap_hit_ratio, sum(idx_blks_hit)::float / sum(idx_blks_read + idx_blks_hit) AS avg_idx_hit_ratio, sum(toast_blks_hit)::float / sum(toast_blks_read + toast_blks_hit) AS avg_toast_hit_ratio, sum(tidx_blks_hit)::float / sum(tidx_blks_read + tidx_blks_hit) AS avg_tidx_hit_ratio FROM pg_statio_all_tables
+      0: SELECT sum(heap_blks_read)::float / NULLIF(sum(heap_blks_read + heap_blks_hit), 0) AS avg_heap_hit_ratio, sum(idx_blks_hit)::float / NULLIF(sum(idx_blks_read + idx_blks_hit), 0) AS avg_idx_hit_ratio, sum(toast_blks_hit)::float / NULLIF(sum(toast_blks_read + toast_blks_hit), 0) AS avg_toast_hit_ratio, sum(tidx_blks_hit)::float / NULLIF(sum(tidx_blks_read + tidx_blks_hit), 0) AS avg_tidx_hit_ratio FROM pg_statio_all_tables
 
   # Debugging
   ntables: