diff --git a/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java b/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
index cebf15021fe..7f4147c02c0 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
@@ -503,10 +503,7 @@ public class AutoBuild {
 					typeScriptFiles.add(sourcePath.toFile());
 				}
 			}
-			tsParser.prepareFiles(typeScriptFiles);
-			for (File file : typeScriptFiles) {
-				extract(extractor, file.toPath());
-			}
+			extractTypeScriptFiles(typeScriptFiles, extractedFiles, extractor);
 			tsParser.closeProject(projectFile);
 		}
 
@@ -524,13 +521,7 @@ public class AutoBuild {
 			}
 		}
 		if (!remainingTypeScriptFiles.isEmpty()) {
-			tsParser.prepareFiles(remainingTypeScriptFiles);
-			for (File f : remainingTypeScriptFiles) {
-				Path path = f.toPath();
-				if (extractedFiles.add(path)) {
-					extract(extractor, path);
-				}
-			}
+			extractTypeScriptFiles(remainingTypeScriptFiles, extractedFiles, extractor);
 		}
 
 		// The TypeScript compiler instance is no longer needed.
@@ -552,6 +543,16 @@ public class AutoBuild {
 		extractorState.getTypeScriptParser().verifyInstallation(true);
 	}
 
+	public void extractTypeScriptFiles(List<File> files, Set<Path> extractedFiles, FileExtractor extractor) throws IOException {
+		extractorState.getTypeScriptParser().prepareFiles(files);
+		for (File f : files) {
+			Path path = f.toPath();
+			if (extractedFiles.add(path)) {
+				extract(extractor, f.toPath());
+			}
+		}
+	}
+
 	private Path normalizePath(Path path) {
 		return path.toAbsolutePath().normalize();
 	}
diff --git a/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java b/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
index 89d9494b404..7969c093f4e 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
@@ -1,5 +1,6 @@
 package com.semmle.js.extractor.test;
 
+import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
@@ -100,6 +101,13 @@ public class AutoBuildTests {
 				@Override
 				public void verifyTypeScriptInstallation() {
 				}
+
+				@Override
+				public void extractTypeScriptFiles(List<File> files, Set<Path> extractedFiles, FileExtractor extractor) throws IOException {
+					for (File f : files) {
+						actual.add(f.toString());
+					}
+				}
 			}.run();
 			String expectedString = StringUtil.glue("\n", expected.stream().sorted().toArray());
 			String actualString = StringUtil.glue("\n", actual.stream().sorted().toArray());