diff --git a/pkg/store/cache/cache.go b/pkg/store/cache/cache.go
index 4e5bcf87dd..82bf30625e 100644
--- a/pkg/store/cache/cache.go
+++ b/pkg/store/cache/cache.go
@@ -7,6 +7,7 @@ import (
 	"context"
 	"encoding/base64"
 	"strconv"
+	"strings"
 
 	"github.com/oklog/ulid"
 	"github.com/prometheus/prometheus/model/labels"
@@ -102,7 +103,11 @@ func (c cacheKey) string() string {
 		// which would end up in wrong query results.
 		matchers := c.key.(cacheKeyExpandedPostings)
 		matchersHash := blake2b.Sum256([]byte(matchers))
-		return "EP:" + c.block + ":" + base64.RawURLEncoding.EncodeToString(matchersHash[0:])
+		key := "EP:" + c.block + ":" + base64.RawURLEncoding.EncodeToString(matchersHash[0:])
+		if len(c.compression) > 0 {
+			key += ":" + c.compression
+		}
+		return key
 	case cacheKeySeries:
 		return "S:" + c.block + ":" + strconv.FormatUint(uint64(c.key.(cacheKeySeries)), 10)
 	default:
@@ -111,16 +116,16 @@ func (c cacheKey) string() string {
 }
 
 func labelMatchersToString(matchers []*labels.Matcher) string {
-	matchersString := ""
+	sb := strings.Builder{}
 	for i, lbl := range matchers {
-		matchersString += lbl.String()
+		sb.WriteString(lbl.String())
 		if i < len(matchers)-1 {
-			matchersString += ";"
+			sb.WriteRune(';')
 		}
 	}
-	return matchersString
+	return sb.String()
 }
 
 type cacheKeyPostings labels.Label
-type cacheKeyExpandedPostings string
+type cacheKeyExpandedPostings string // We don't use []*labels.Matcher because it is not a hashable type so fail at inmemory cache.
 type cacheKeySeries uint64
diff --git a/pkg/store/cache/cache_test.go b/pkg/store/cache/cache_test.go
index 778efce1fb..59adf2b8c7 100644
--- a/pkg/store/cache/cache_test.go
+++ b/pkg/store/cache/cache_test.go
@@ -43,12 +43,21 @@ func TestCacheKey_string(t *testing.T) {
 				return fmt.Sprintf("P:%s:%s", uid.String(), encodedHash)
 			}(),
 		},
+		"postings cache key includes compression scheme": {
+			key: cacheKey{ulidString, cacheKeyPostings(labels.Label{Name: "foo", Value: "bar"}), compressionSchemeStreamedSnappy},
+			expected: func() string {
+				hash := blake2b.Sum256([]byte("foo:bar"))
+				encodedHash := base64.RawURLEncoding.EncodeToString(hash[0:])
+
+				return fmt.Sprintf("P:%s:%s:%s", uid.String(), encodedHash, compressionSchemeStreamedSnappy)
+			}(),
+		},
 		"should stringify series cache key": {
 			key:      cacheKey{ulidString, cacheKeySeries(12345), ""},
 			expected: fmt.Sprintf("S:%s:12345", uid.String()),
 		},
 		"should stringify expanded postings cache key": {
-			key: cacheKey{ulidString, cacheKeyExpandedPostings(labelMatchersToString([]*labels.Matcher{matcher}))},
+			key: cacheKey{ulidString, cacheKeyExpandedPostings(labelMatchersToString([]*labels.Matcher{matcher})), ""},
 			expected: func() string {
 				hash := blake2b.Sum256([]byte(matcher.String()))
 				encodedHash := base64.RawURLEncoding.EncodeToString(hash[0:])
@@ -57,7 +66,7 @@ func TestCacheKey_string(t *testing.T) {
 			}(),
 		},
 		"should stringify expanded postings cache key when multiple matchers": {
-			key: cacheKey{ulidString, cacheKeyExpandedPostings(labelMatchersToString([]*labels.Matcher{matcher, matcher2}))},
+			key: cacheKey{ulidString, cacheKeyExpandedPostings(labelMatchersToString([]*labels.Matcher{matcher, matcher2})), ""},
 			expected: func() string {
 				hash := blake2b.Sum256([]byte(fmt.Sprintf("%s;%s", matcher.String(), matcher2.String())))
 				encodedHash := base64.RawURLEncoding.EncodeToString(hash[0:])
@@ -65,6 +74,15 @@ func TestCacheKey_string(t *testing.T) {
 				return fmt.Sprintf("EP:%s:%s", uid.String(), encodedHash)
 			}(),
 		},
+		"expanded postings cache key includes compression scheme": {
+			key: cacheKey{ulidString, cacheKeyExpandedPostings(labelMatchersToString([]*labels.Matcher{matcher})), compressionSchemeStreamedSnappy},
+			expected: func() string {
+				hash := blake2b.Sum256([]byte(matcher.String()))
+				encodedHash := base64.RawURLEncoding.EncodeToString(hash[0:])
+
+				return fmt.Sprintf("EP:%s:%s:%s", uid.String(), encodedHash, compressionSchemeStreamedSnappy)
+			}(),
+		},
 	}
 
 	for testName, testData := range tests {
@@ -110,7 +128,7 @@ func TestCacheKey_string_ShouldGuaranteeReasonablyShortKeyLength(t *testing.T) {
 						matchers = append(matchers, labels.MustNewMatcher(t, name, value))
 					}
 					return cacheKeyExpandedPostings(labelMatchersToString(matchers))
-				}()},
+				}(), ""},
 			},
 		},
 	}
diff --git a/pkg/store/cache/inmemory.go b/pkg/store/cache/inmemory.go
index a73a5d64df..8e35f4dca3 100644
--- a/pkg/store/cache/inmemory.go
+++ b/pkg/store/cache/inmemory.go
@@ -326,7 +326,7 @@ func (c *InMemoryIndexCache) StoreExpandedPostings(blockID ulid.ULID, matchers [
 
 // FetchExpandedPostings fetches expanded postings and returns cached data and a boolean value representing whether it is a cache hit or not.
 func (c *InMemoryIndexCache) FetchExpandedPostings(_ context.Context, blockID ulid.ULID, matchers []*labels.Matcher) ([]byte, bool) {
-	if b, ok := c.get(cacheTypeExpandedPostings, cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(matchers))}); ok {
+	if b, ok := c.get(cacheTypeExpandedPostings, cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(matchers)), ""}); ok {
 		return b, true
 	}
 	return nil, false
diff --git a/pkg/store/cache/memcached.go b/pkg/store/cache/memcached.go
index 856adb03f3..4f0807ecbd 100644
--- a/pkg/store/cache/memcached.go
+++ b/pkg/store/cache/memcached.go
@@ -123,7 +123,7 @@ func (c *RemoteIndexCache) FetchMultiPostings(ctx context.Context, blockID ulid.
 // The function enqueues the request and returns immediately: the entry will be
 // asynchronously stored in the cache.
 func (c *RemoteIndexCache) StoreExpandedPostings(blockID ulid.ULID, keys []*labels.Matcher, v []byte) {
-	key := cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(keys))}.string()
+	key := cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(keys)), ""}.string()
 
 	if err := c.memcached.SetAsync(key, v, memcachedDefaultTTL); err != nil {
 		level.Error(c.logger).Log("msg", "failed to cache expanded postings in memcached", "err", err)
@@ -134,7 +134,7 @@ func (c *RemoteIndexCache) StoreExpandedPostings(blockID ulid.ULID, keys []*labe
 // and returns a map containing cache hits, along with a list of missing keys.
 // In case of error, it logs and return an empty cache hits map.
 func (c *RemoteIndexCache) FetchExpandedPostings(ctx context.Context, blockID ulid.ULID, lbls []*labels.Matcher) ([]byte, bool) {
-	key := cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(lbls))}.string()
+	key := cacheKey{blockID.String(), cacheKeyExpandedPostings(labelMatchersToString(lbls)), ""}.string()
 
 	// Fetch the keys from memcached in a single request.
 	c.expandedPostingRequests.Add(1)