diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.aggregation/30_sig_terms.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.aggregation/30_sig_terms.yml
index d7759afe4a907..05fdb6a80b856 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.aggregation/30_sig_terms.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.aggregation/30_sig_terms.yml
@@ -73,6 +73,87 @@
   - match: {aggregations.class.buckets.1.sig_terms.buckets.0.key: "good"}
 
 ---
+"Test background filter count ":
+  - skip:
+      version: " - 7.14.99"
+      reason: bugfix introduced in 7.15.0
+
+  - do:
+      indices.create:
+        index:  goodbad
+        body:
+          settings:
+            number_of_shards: "1"
+          mappings:
+            properties:
+              text:
+                type: text
+                fielddata: true
+              class:
+                type: keyword
+  - do:
+      indices.create:
+        index: goodbad-2
+        body:
+          settings:
+            number_of_shards: "1"
+          mappings:
+            properties:
+              text:
+                type: text
+                fielddata: true
+              class:
+                type: keyword
+
+  - do:
+      index:
+        index: goodbad-2
+        id: 1
+        body: { class: "bad" }
+  - do:
+      index:
+        index: goodbad-2
+        id: 2
+        body: { class: "bad" }
+
+  - do:
+      index:
+        index:  goodbad
+        id:     1
+        body:   { text: "good", class: "good" }
+  - do:
+      index:
+        index:  goodbad
+        id:     2
+        body:   { text: "good", class: "good" }
+  - do:
+      index:
+        index:  goodbad
+        id:     3
+        body:   { text: "bad", class: "bad" }
+  - do:
+      index:
+        index:  goodbad
+        id:     4
+        body:   { text: "bad", class: "bad" }
+
+  - do:
+      indices.refresh:
+        index: [goodbad, goodbad-2]
+
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        index: goodbad*
+
+  - match: {hits.total: 6}
+
+  - do:
+      search:
+        index: goodbad*
+        body: {"aggs": {"sig_terms": {"significant_terms": {"field": "text", "background_filter": {"bool": {"filter": [{"term": {"class": "good" }}]}}}}}}
+  - match: { aggregations.sig_terms.bg_count: 2 }
+---
 "IP test":
   - do:
       indices.create:
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/AbstractStringTermsAggregator.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/AbstractStringTermsAggregator.java
index aadec9b36e330..263f6752c31e1 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/AbstractStringTermsAggregator.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/AbstractStringTermsAggregator.java
@@ -36,9 +36,12 @@ protected StringTerms buildEmptyTermsAggregation() {
                 metadata(), format, bucketCountThresholds.getShardSize(), showTermDocCountError, 0, emptyList(), 0L);
     }
 
-    protected SignificantStringTerms buildEmptySignificantTermsAggregation(long subsetSize, SignificanceHeuristic significanceHeuristic) {
+    protected SignificantStringTerms buildEmptySignificantTermsAggregation(
+        long subsetSize,
+        long supersetSize,
+        SignificanceHeuristic significanceHeuristic
+    ) {
         // We need to account for the significance of a miss in our global stats - provide corpus size as context
-        int supersetSize = searcher().getIndexReader().numDocs();
         return new SignificantStringTerms(name, bucketCountThresholds.getRequiredSize(), bucketCountThresholds.getMinDocCount(),
                 metadata(), format, subsetSize, supersetSize, significanceHeuristic, emptyList());
     }
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/GlobalOrdinalsStringTermsAggregator.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/GlobalOrdinalsStringTermsAggregator.java
index e4d44114166ca..7c9947c0d780a 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/GlobalOrdinalsStringTermsAggregator.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/GlobalOrdinalsStringTermsAggregator.java
@@ -894,12 +894,12 @@ SignificantStringTerms buildResult(long owningBucketOrd, long otherDocCount, Sig
 
         @Override
         SignificantStringTerms buildEmptyResult() {
-            return buildEmptySignificantTermsAggregation(0, significanceHeuristic);
+            return buildEmptySignificantTermsAggregation(0, supersetSize, significanceHeuristic);
         }
 
         @Override
         SignificantStringTerms buildNoValuesResult(long owningBucketOrdinal) {
-            return buildEmptySignificantTermsAggregation(subsetSizes.get(owningBucketOrdinal), significanceHeuristic);
+            return buildEmptySignificantTermsAggregation(subsetSizes.get(owningBucketOrdinal), supersetSize, significanceHeuristic);
         }
 
         @Override
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/MapStringTermsAggregator.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/MapStringTermsAggregator.java
index a7911bcdc3590..e61cad1458915 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/MapStringTermsAggregator.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/MapStringTermsAggregator.java
@@ -568,7 +568,7 @@ SignificantStringTerms buildResult(long owningBucketOrd, long otherDocCount, Sig
 
         @Override
         SignificantStringTerms buildEmptyResult() {
-            return buildEmptySignificantTermsAggregation(0, significanceHeuristic);
+            return buildEmptySignificantTermsAggregation(0, supersetSize, significanceHeuristic);
         }
 
         @Override
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/NumericTermsAggregator.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/NumericTermsAggregator.java
index 38338bc8e5668..51c73c12b683e 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/NumericTermsAggregator.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/NumericTermsAggregator.java
@@ -573,8 +573,6 @@ SignificantLongTerms buildResult(long owningBucketOrd, long otherDocCoun, Signif
 
         @Override
         SignificantLongTerms buildEmptyResult() {
-            // We need to account for the significance of a miss in our global stats - provide corpus size as context
-            int supersetSize = searcher().getIndexReader().numDocs();
             return new SignificantLongTerms(
                 name,
                 bucketCountThresholds.getRequiredSize(),