diff --git a/src/babel/preval-extract/__tests__/extractStyles.spec.js b/src/babel/preval-extract/__tests__/extractStyles.spec.js
index 9599f34b8..d2c3b49d7 100644
--- a/src/babel/preval-extract/__tests__/extractStyles.spec.js
+++ b/src/babel/preval-extract/__tests__/extractStyles.spec.js
@@ -148,6 +148,37 @@ describe('preval-extract/extractStyles module', () => {
       expect(program.node.body.length).toBe(1);
     });
 
+    it('should append classnames when writing to single file', () => {
+      const writeFileSync = jest.fn();
+      const opts = { single: true, filename: 'A.css' };
+
+      getCachedModule.mockImplementationOnce(
+        getCachedModuleImpl('.classname{color: #ffffff}')
+      );
+
+      extractStyles(types, null, 'file1.js', opts, { writeFileSync });
+
+      getCachedModule.mockImplementationOnce(
+        getCachedModuleImpl('.other{color: #000000}')
+      );
+
+      extractStyles(types, null, 'file2.js', opts, { writeFileSync });
+
+      expect(fs.writeFileSync).toHaveBeenCalledTimes(2);
+      expect(fs.writeFileSync.mock.calls[0][0]).toEqual(
+        path.join(process.cwd(), 'A.css')
+      );
+      expect(fs.writeFileSync.mock.calls[0][1]).toMatch(
+        '.classname{color: #ffffff}'
+      );
+      expect(fs.writeFileSync.mock.calls[1][0]).toEqual(
+        path.join(process.cwd(), 'A.css')
+      );
+      expect(fs.writeFileSync.mock.calls[1][1]).toMatch(
+        '.classname{color: #ffffff}\n.other{color: #000000}'
+      );
+    });
+
     it('should overwrite if the file has changed', () => {
       getCachedModule.mockImplementationOnce(
         getCachedModuleImpl('.classname{color: #ffffff}')
diff --git a/src/babel/preval-extract/extractStyles.js b/src/babel/preval-extract/extractStyles.js
index 0298ac2eb..fe685422d 100644
--- a/src/babel/preval-extract/extractStyles.js
+++ b/src/babel/preval-extract/extractStyles.js
@@ -10,7 +10,7 @@ import { getCachedModule } from '../lib/moduleSystem';
 const preamble =
   '/* THIS FILE IS AUTOGENERATED. DO NOT EDIT IT DIRECTLY, NOR COMMIT IT TO VERSION CONTROL. */';
 
-function parseCurrentFilename(filename: string, outDir: string) {
+function parseCurrentFilename(filename: string, outDir: string = '') {
   const dirname = path.isAbsolute(filename)
     ? path.dirname(filename)
     : path.join(process.cwd(), outDir);
@@ -21,7 +21,7 @@ function parseCurrentFilename(filename: string, outDir: string) {
 function parseFilename(
   filename: string,
   currentFilename: string,
-  outDir: string
+  outDir: string = ''
 ) {
   const dirname = path.isAbsolute(outDir)
     ? outDir
@@ -75,8 +75,8 @@ export default function extractStyles(
     single: false,
     ...options,
     filename: options.filename
-      ? parseFilename(options.filename, currentFilename, options.outDir || '')
-      : parseCurrentFilename(currentFilename, options.outDir || ''),
+      ? parseFilename(options.filename, currentFilename, options.outDir)
+      : parseCurrentFilename(currentFilename, options.outDir),
   };
 
   if (!extract) {
@@ -90,16 +90,19 @@ export default function extractStyles(
     return;
   }
 
-  if (cache && hasCachedStyles(filename, data)) {
-    if (!single) {
-      addRequireForCss(types, program, filename);
-    }
-
-    return;
-  }
-
   if (cache) {
-    stylesCache[filename] = data;
+    if (single) {
+      if (hasCachedStyles(currentFilename, data)) {
+        return;
+      }
+      stylesCache[currentFilename] = data;
+    } else {
+      if (hasCachedStyles(filename, data)) {
+        addRequireForCss(types, program, filename);
+        return;
+      }
+      stylesCache[filename] = data;
+    }
   }
 
   if (single) {