diff --git a/IDE/src/BuildContext.bf b/IDE/src/BuildContext.bf
index fb94ad87..871fb8dd 100644
--- a/IDE/src/BuildContext.bf
+++ b/IDE/src/BuildContext.bf
@@ -1262,6 +1262,9 @@ namespace IDE
 
 		    Workspace.Options workspaceOptions = gApp.GetCurWorkspaceOptions();
 		    BfCompiler bfCompiler = gApp.mBfBuildCompiler;
+			BfSystem bfSystem = gApp.mBfBuildSystem;
+
+			bfSystem.Lock(0);
 		    var bfProject = gApp.mBfBuildSystem.mProjectMap[project];
 		    bool bfHadOutputChanges = false;
 		    List<String> bfFileNames = scope List<String>();
@@ -1284,6 +1287,8 @@ namespace IDE
 				bfCompiler.GetOutputFileNames(bfProject, .FlushQueuedHotFiles, out bfHadOutputChanges, bfFileNames);
 				defer:: ClearAndDeleteItems(bfFileNames);
 			}
+			bfSystem.Unlock();
+
 		    if (bfHadOutputChanges)
 		        project.mNeedsTargetRebuild = true;
 
diff --git a/IDE/src/IDEApp.bf b/IDE/src/IDEApp.bf
index 34f2fd9d..f7b3d79b 100644
--- a/IDE/src/IDEApp.bf
+++ b/IDE/src/IDEApp.bf
@@ -10400,10 +10400,16 @@ namespace IDE
 		        return;
 		    
 		    BfCompiler bfCompiler = mBfBuildCompiler;
+			BfSystem bfSystem = mBfBuildSystem;
+
 		    var bfProject = mBfBuildSystem.mProjectMap[project];
 		    bool bfHadOutputChanges;
 		    List<String> bfFileNames = scope List<String>();
+
+			bfSystem.Lock(0);
 			bfCompiler.GetOutputFileNames(bfProject, .None, out bfHadOutputChanges, bfFileNames);
+			bfSystem.Unlock();
+
 			defer ClearAndDeleteItems(bfFileNames);
 		    if (bfHadOutputChanges)
 		        project.mNeedsTargetRebuild = true;
diff --git a/IDEHelper/Compiler/BfCompiler.cpp b/IDEHelper/Compiler/BfCompiler.cpp
index bfc0127d..0c931410 100644
--- a/IDEHelper/Compiler/BfCompiler.cpp
+++ b/IDEHelper/Compiler/BfCompiler.cpp
@@ -10431,8 +10431,10 @@ enum BfUsedOutputFlags
 
 BF_EXPORT const char* BF_CALLTYPE BfCompiler_GetUsedOutputFileNames(BfCompiler* bfCompiler, BfProject* bfProject, BfUsedOutputFlags flags, bool* hadOutputChanges)
 {	
-	BP_ZONE("BfCompiler_GetUsedOutputFileNames");
+	bfCompiler->mSystem->AssertWeHaveLock();
 
+	BP_ZONE("BfCompiler_GetUsedOutputFileNames");
+	
 	*hadOutputChanges = false;
 	String& outString = *gTLStrReturn.Get();
 	outString.clear();