diff --git a/include/slang/ast/ASTContext.h b/include/slang/ast/ASTContext.h
index f1df6cf8c..708606d2c 100644
--- a/include/slang/ast/ASTContext.h
+++ b/include/slang/ast/ASTContext.h
@@ -232,8 +232,7 @@ struct SLANG_EXPORT AssertionInstanceDetails {
     SourceLocation instanceLoc;
 
     /// A map of formal argument symbols to their actual replacements.
-    map_with_incomplete_type<const Symbol*,
-                             std::tuple<const syntax::PropertyExprSyntax*, ASTContext>>
+    flat_hash_map<const Symbol*, std::tuple<const syntax::PropertyExprSyntax*, ASTContext>>
         argumentMap;
 
     /// A map of local variables declared in the assertion item.
diff --git a/include/slang/ast/Compilation.h b/include/slang/ast/Compilation.h
index 79cffad62..31b1f56e1 100644
--- a/include/slang/ast/Compilation.h
+++ b/include/slang/ast/Compilation.h
@@ -176,7 +176,7 @@ struct HierarchyOverrideNode {
         overrides;
 
     /// A map of child scopes that also contain overrides.
-    map_with_incomplete_type<InstancePath::Entry, HierarchyOverrideNode> childNodes;
+    flat_hash_map<InstancePath::Entry, HierarchyOverrideNode> childNodes;
 
     /// A list of bind directives to apply in this scope.
     std::vector<const syntax::BindDirectiveSyntax*> binds;
diff --git a/include/slang/util/Hash.h b/include/slang/util/Hash.h
index e75388c9b..4d33f7305 100644
--- a/include/slang/util/Hash.h
+++ b/include/slang/util/Hash.h
@@ -387,10 +387,6 @@ template<typename T, typename H = hash<T>, typename E = std::equal_to<T>,
          typename A = std::allocator<T>>
 using flat_node_set = boost::unordered_node_set<T, H, E, A>;
 
-template<typename K, typename V, typename H = hash<K>, typename E = std::equal_to<K>,
-         typename A = std::allocator<std::pair<const K, V>>>
-using map_with_incomplete_type = boost::unordered_flat_map<K, V, H, E, A>;
-
 /// A hash map container that allocates room for its first `N` elements on the stack.
 /// Prefer this over a normal hash map for temporary stack variables and small maps
 /// where heap allocations can be avoided.