diff --git a/pkg/apis/psmdb/v1/psmdb_defaults.go b/pkg/apis/psmdb/v1/psmdb_defaults.go
index 4e41f089c..a24fe7a65 100644
--- a/pkg/apis/psmdb/v1/psmdb_defaults.go
+++ b/pkg/apis/psmdb/v1/psmdb_defaults.go
@@ -727,6 +727,16 @@ func (rs *ReplsetSpec) SetDefaults(platform version.Platform, cr *PerconaServerM
 		}
 	}
 
+	if rs.Storage != nil && rs.Storage.Engine == StorageEngineInMemory {
+		encryptionEnabled, err := rs.Configuration.IsEncryptionEnabled()
+		if err != nil {
+			return errors.Wrap(err, "failed to parse replset configuration")
+		}
+		if encryptionEnabled != nil && *encryptionEnabled {
+			return errors.New("inMemory storage engine doesn't support encryption")
+		}
+	}
+
 	return nil
 }
 
diff --git a/pkg/psmdb/statefulset.go b/pkg/psmdb/statefulset.go
index c4aab9968..dfdbe6bc9 100644
--- a/pkg/psmdb/statefulset.go
+++ b/pkg/psmdb/statefulset.go
@@ -584,7 +584,11 @@ func isEncryptionEnabled(cr *api.PerconaServerMongoDB, replset *api.ReplsetSpec)
 	if err != nil {
 		return false, errors.Wrap(err, "failed to parse replset configuration")
 	}
+
 	if enabled == nil {
+		if replset.Storage.Engine == api.StorageEngineInMemory {
+			return false, nil // disabled for inMemory engine by default
+		}
 		return true, nil // true by default
 	}
 	return *enabled, nil