diff --git a/source/frontend/collector.cpp b/source/frontend/collector.cpp
index be3a672c..1e0b06ea 100644
--- a/source/frontend/collector.cpp
+++ b/source/frontend/collector.cpp
@@ -93,13 +93,13 @@ namespace frontend
 			// note that we're guaranteed (because that's the whole point)
 			// that any module we encounter here will have had all of its dependencies checked already
 
-			std::vector<std::pair<ImportThing, sst::StateTree*>> imports;
+			std::vector<std::pair<ImportThing, sst::DefinitionTree*>> imports;
 			for(auto d : state->graph->getDependenciesOf(file))
 			{
 				auto imported = d->to;
 
-				auto stree = state->dtrees[imported->name]->base;
-				iceAssert(stree);
+				auto dtree = state->dtrees[imported->name];
+				iceAssert(dtree);
 
 				ImportThing ithing { imported->name, d->ithing.importAs, d->ithing.pubImport, d->ithing.loc };
 				if(auto it = std::find_if(imports.begin(), imports.end(), [&ithing](const auto& x) -> bool { return x.first.name == ithing.name; });
@@ -110,7 +110,7 @@ namespace frontend
 						->postAndQuit();
 				}
 
-				imports.push_back({ ithing, stree });
+				imports.push_back({ ithing, dtree });
 			}
 
 			// i guess we always add prelude definitions?
diff --git a/source/frontend/file.cpp b/source/frontend/file.cpp
index 388ab41e..178a46e3 100644
--- a/source/frontend/file.cpp
+++ b/source/frontend/file.cpp
@@ -25,7 +25,6 @@ namespace frontend
 		std::vector<size_t> importIndices;
 
 		bool didLex = false;
-		bool isLexing = false;
 	};
 
 	static util::hash_map<std::string, FileInnards> fileList;
@@ -35,7 +34,7 @@ namespace frontend
 		// break early if we can
 		{
 			auto it = fileList.find(fullPath);
-			if(it != fileList.end() && it->second.didLex)
+			if(it != fileList.end())
 				return it->second;
 		}
 
@@ -89,21 +88,13 @@ namespace frontend
 			}
 		}
 
-
 		Location pos;
 		FileInnards& innards = fileList[fullPath];
-		if(innards.isLexing)
-		{
-			warn("attempting to lex file while file is already being lexed, stop it");
-			return innards;
-		}
-
 		{
 			pos.fileID = getFileIDFromFilename(fullPath);
 
 			innards.fileContents = std::move(fileContents);
 			innards.lines = std::move(rawlines);
-			innards.isLexing = true;
 		}
 
 		lexer::TokenList& ts = innards.tokens;
@@ -133,7 +124,6 @@ namespace frontend
 		}
 
 		innards.didLex = true;
-		innards.isLexing = false;
 		return innards;
 	}
 
diff --git a/source/include/typecheck.h b/source/include/typecheck.h
index c6c65c27..a8e4b0f1 100644
--- a/source/include/typecheck.h
+++ b/source/include/typecheck.h
@@ -110,14 +110,14 @@ namespace sst
 
 	struct TypecheckState
 	{
-		TypecheckState(StateTree* st) : dtree(new DefinitionTree(st)), stree(dtree->base) { }
+		TypecheckState(StateTree* st) : dtree(new DefinitionTree(st)), stree(dtree->base), typeDefnMap(dtree->typeDefnMap) { }
 
 		std::string moduleName;
 
 		DefinitionTree* dtree = 0;
 		StateTree* stree = 0;
 
-		util::hash_map<fir::Type*, TypeDefn*> typeDefnMap;
+		util::hash_map<fir::Type*, TypeDefn*>& typeDefnMap;
 
 		std::vector<Location> locationStack;
 
@@ -207,7 +207,7 @@ namespace sst
 	};
 
 	DefinitionTree* typecheck(frontend::CollectorState* cs, const parser::ParsedFile& file,
-		const std::vector<std::pair<frontend::ImportThing, StateTree*>>& imports, bool addPreludeDefinitions);
+		const std::vector<std::pair<frontend::ImportThing, DefinitionTree*>>& imports, bool addPreludeDefinitions);
 
 
 	StateTree* addTreeToExistingTree(StateTree* to, StateTree* from, StateTree* commonParent, bool pubImport, bool ignoreVis);
diff --git a/source/typecheck/dotop.cpp b/source/typecheck/dotop.cpp
index 4a0c7460..5352dfe2 100644
--- a/source/typecheck/dotop.cpp
+++ b/source/typecheck/dotop.cpp
@@ -462,6 +462,7 @@ static sst::Expr* doExpressionDotOp(sst::TypecheckState* fs, ast::DotOperator* d
 
 	// ok.
 	auto defn = fs->typeDefnMap[type];
+	iceAssert(defn);
 
 	if(auto str = dcast(sst::StructDefn, defn))
 	{
diff --git a/source/typecheck/toplevel.cpp b/source/typecheck/toplevel.cpp
index 705ccf51..77fa4271 100644
--- a/source/typecheck/toplevel.cpp
+++ b/source/typecheck/toplevel.cpp
@@ -296,8 +296,8 @@ namespace sst
 
 
 	using frontend::CollectorState;
-	DefinitionTree* typecheck(CollectorState* cs, const parser::ParsedFile& file, const std::vector<std::pair<frontend::ImportThing, StateTree*>>& imports,
-		bool addPreludeDefinitions)
+	DefinitionTree* typecheck(CollectorState* cs, const parser::ParsedFile& file,
+		const std::vector<std::pair<frontend::ImportThing, DefinitionTree*>>& imports, bool addPreludeDefinitions)
 	{
 		StateTree* tree = new StateTree(file.moduleName, file.name, 0);
 		tree->treeDefn = util::pool<TreeDefn>(Location());
@@ -357,10 +357,11 @@ namespace sst
 
 			iceAssert(insertPoint);
 
-			_addTreeToExistingTree(fs->dtree->thingsImported, insertPoint, import, /* commonParent: */ nullptr, ithing.pubImport,
+			_addTreeToExistingTree(fs->dtree->thingsImported, insertPoint, import->base, /* commonParent: */ nullptr, ithing.pubImport,
 				/* ignoreVis: */ false, file.name);
 
 			fs->dtree->thingsImported.insert(ithing.name);
+			fs->dtree->typeDefnMap.insert(import->typeDefnMap.begin(), import->typeDefnMap.end());
 		}
 
 		if(addPreludeDefinitions)
@@ -372,8 +373,6 @@ namespace sst
 		tns->name = file.moduleName;
 
 		fs->dtree->topLevel = tns;
-
-		fs->dtree->typeDefnMap = fs->typeDefnMap;
 		return fs->dtree;
 	}
 }