diff --git a/source/common/upstream/load_balancer_impl.cc b/source/common/upstream/load_balancer_impl.cc
index 742978bf4f2f..226b24220fae 100644
--- a/source/common/upstream/load_balancer_impl.cc
+++ b/source/common/upstream/load_balancer_impl.cc
@@ -775,5 +775,35 @@ HostConstSharedPtr RandomLoadBalancer::chooseHostOnce(LoadBalancerContext* conte
   return hosts_to_use[random_.random() % hosts_to_use.size()];
 }
 
+SubsetSelectorImpl::SubsetSelectorImpl(
+    const Protobuf::RepeatedPtrField<std::string>& selector_keys,
+    envoy::api::v2::Cluster::LbSubsetConfig::LbSubsetSelector::LbSubsetSelectorFallbackPolicy
+        fallback_policy,
+    const Protobuf::RepeatedPtrField<std::string>& fallback_keys_subset)
+    : selector_keys_(selector_keys.begin(), selector_keys.end()), fallback_policy_(fallback_policy),
+      fallback_keys_subset_(fallback_keys_subset.begin(), fallback_keys_subset.end()) {
+
+  if (fallback_policy_ != envoy::api::v2::Cluster::LbSubsetConfig::LbSubsetSelector::KEYS_SUBSET) {
+    if (!fallback_keys_subset_.empty()) {
+      throw EnvoyException("fallback_keys_subset can be set only for KEYS_SUBSET fallback_policy");
+    }
+    return;
+  }
+
+  if (fallback_keys_subset_.empty()) {
+    throw EnvoyException("fallback_keys_subset cannot be empty");
+  }
+
+  if (!std::includes(selector_keys_.begin(), selector_keys_.end(), fallback_keys_subset_.begin(),
+                     fallback_keys_subset_.end())) {
+    throw EnvoyException("fallback_keys_subset must be a subset of selector keys");
+  }
+
+  // Enforce that the fallback_keys_subset_ set is smaller than the selector_keys_ set. Otherwise
+  // we could end up with a infinite recursion of SubsetLoadBalancer::chooseHost().
+  if (selector_keys_.size() == fallback_keys_subset_.size()) {
+    throw EnvoyException("fallback_keys_subset cannot be equal to keys");
+  }
+}
 } // namespace Upstream
 } // namespace Envoy
diff --git a/source/common/upstream/load_balancer_impl.h b/source/common/upstream/load_balancer_impl.h
index 7f8e4bbbce9e..f2d71fb092c9 100644
--- a/source/common/upstream/load_balancer_impl.h
+++ b/source/common/upstream/load_balancer_impl.h
@@ -489,35 +489,7 @@ class SubsetSelectorImpl : public SubsetSelector {
       const Protobuf::RepeatedPtrField<std::string>& selector_keys,
       envoy::api::v2::Cluster::LbSubsetConfig::LbSubsetSelector::LbSubsetSelectorFallbackPolicy
           fallback_policy,
-      const Protobuf::RepeatedPtrField<std::string>& fallback_keys_subset)
-      : selector_keys_(selector_keys.begin(), selector_keys.end()),
-        fallback_policy_(fallback_policy),
-        fallback_keys_subset_(fallback_keys_subset.begin(), fallback_keys_subset.end()) {
-
-    if (fallback_policy_ !=
-        envoy::api::v2::Cluster::LbSubsetConfig::LbSubsetSelector::KEYS_SUBSET) {
-      if (!fallback_keys_subset_.empty()) {
-        throw EnvoyException(
-            "fallback_keys_subset can be set only for KEYS_SUBSET fallback_policy");
-      }
-      return;
-    }
-
-    if (fallback_keys_subset_.empty()) {
-      throw EnvoyException("fallback_keys_subset cannot be empty");
-    }
-
-    if (!std::includes(selector_keys_.begin(), selector_keys_.end(), fallback_keys_subset_.begin(),
-                       fallback_keys_subset_.end())) {
-      throw EnvoyException("fallback_keys_subset must be a subset of selector keys");
-    }
-
-    // Enforce that the fallback_keys_subset_ set is smaller than the selector_keys_ set. Otherwise
-    // we could end up with a infinite recursion of SubsetLoadBalancer::chooseHost().
-    if (selector_keys_.size() == fallback_keys_subset_.size()) {
-      throw EnvoyException("fallback_keys_subset cannot be equal to keys");
-    }
-  }
+      const Protobuf::RepeatedPtrField<std::string>& fallback_keys_subset);
 
   // SubsetSelector
   const std::set<std::string>& selectorKeys() const override { return selector_keys_; }