diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5fe58311d75..6f510ce659a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,24 @@
 # Changelog
 
+## Unreleased
+
+* Fix importing a path containing a `?` character on Windows ([#989](https://github.com/evanw/esbuild/issues/989))
+
+    On Windows, the `?` character is not allowed in path names. This causes esbuild to fail to import paths containing this character. This is usually fine because people don't put `?` in their file names for this reason. However, the import paths for some ancient CSS code contains the `?` character as a hack to work around a bug in Internet Explorer:
+
+    ```css
+    @font-face {
+      src:
+        url("./icons.eot?#iefix") format('embedded-opentype'),
+        url("./icons.woff2") format('woff2'),
+        url("./icons.woff") format('woff'),
+        url("./icons.ttf") format('truetype'),
+        url("./icons.svg#icons") format('svg');
+    }
+    ```
+
+    The intent is for the bundler to ignore the `?#iefix` part. However, there may actually be a file called `icons.eot?#iefix` on the file system so esbuild checks the file system for both `icons.eot?#iefix` and `icons.eot`. This check was triggering this issue. With this release, an invalid path is considered the same as a missing file so bundling code like this should now work on Windows.
+
 ## 0.9.3
 
 * Fix path resolution with the `exports` field for scoped packages
diff --git a/internal/fs/fs_real.go b/internal/fs/fs_real.go
index 8a8e46e0b6c..0089e93bddd 100644
--- a/internal/fs/fs_real.go
+++ b/internal/fs/fs_real.go
@@ -131,7 +131,7 @@ func (fs *realFS) ReadDirectory(dir string) (DirEntries, error) {
 	}
 
 	// Cache miss: read the directory entries
-	names, err := readdir(dir)
+	names, err := fs.readdir(dir)
 	entries := DirEntries{dir, make(map[string]*Entry)}
 
 	// Unwrap to get the underlying error
@@ -184,19 +184,7 @@ func (fs *realFS) ReadFile(path string) (string, error) {
 	BeforeFileOpen()
 	defer AfterFileClose()
 	buffer, err := ioutil.ReadFile(path)
-
-	// Unwrap to get the underlying error
-	if pathErr, ok := err.(*os.PathError); ok {
-		err = pathErr.Unwrap()
-	}
-
-	// Windows returns ENOTDIR here even though nothing we've done yet has asked
-	// for a directory. This really means ENOENT on Windows. Return ENOENT here
-	// so callers that check for ENOENT will successfully detect this file as
-	// missing.
-	if err == syscall.ENOTDIR {
-		err = syscall.ENOENT
-	}
+	err = fs.canonicalizeError(err)
 
 	// Allocate the string once
 	fileContents := string(buffer)
@@ -282,23 +270,11 @@ func (fs *realFS) Rel(base string, target string) (string, bool) {
 	return "", false
 }
 
-func readdir(dirname string) ([]string, error) {
+func (fs *realFS) readdir(dirname string) ([]string, error) {
 	BeforeFileOpen()
 	defer AfterFileClose()
 	f, err := os.Open(dirname)
-
-	// Unwrap to get the underlying error
-	if pathErr, ok := err.(*os.PathError); ok {
-		err = pathErr.Unwrap()
-	}
-
-	// Windows returns ENOTDIR here even though nothing we've done yet has asked
-	// for a directory. This really means ENOENT on Windows. Return ENOENT here
-	// so callers that check for ENOENT will successfully detect this directory
-	// as missing.
-	if err == syscall.ENOTDIR {
-		return nil, syscall.ENOENT
-	}
+	err = fs.canonicalizeError(err)
 
 	// Stop now if there was an error
 	if err != nil {
@@ -319,6 +295,34 @@ func readdir(dirname string) ([]string, error) {
 	return entries, err
 }
 
+func (fs *realFS) canonicalizeError(err error) error {
+	// Unwrap to get the underlying error
+	if pathErr, ok := err.(*os.PathError); ok {
+		err = pathErr.Unwrap()
+	}
+
+	// This has been copied from golang.org/x/sys/windows
+	const ERROR_INVALID_NAME syscall.Errno = 123
+
+	// Windows is much more restrictive than Unix about file names. If a file name
+	// is invalid, it will return ERROR_INVALID_NAME. Treat this as ENOENT (i.e.
+	// "the file does not exist") so that the resolver continues trying to resolve
+	// the path on this failure instead of aborting with an error.
+	if fs.fp.isWindows && err == ERROR_INVALID_NAME {
+		err = syscall.ENOENT
+	}
+
+	// Windows returns ENOTDIR here even though nothing we've done yet has asked
+	// for a directory. This really means ENOENT on Windows. Return ENOENT here
+	// so callers that check for ENOENT will successfully detect this file as
+	// missing.
+	if err == syscall.ENOTDIR {
+		err = syscall.ENOENT
+	}
+
+	return err
+}
+
 func (fs *realFS) kind(dir string, base string) (symlink string, kind EntryKind) {
 	entryPath := fs.fp.join([]string{dir, base})
 
@@ -401,7 +405,7 @@ func (fs *realFS) WatchData() WatchData {
 
 		case stateDirHasEntries:
 			paths[path] = func() bool {
-				names, err := readdir(path)
+				names, err := fs.readdir(path)
 				if err != nil || len(names) != len(data.dirEntries) {
 					return true
 				}
diff --git a/scripts/end-to-end-tests.js b/scripts/end-to-end-tests.js
index 583c222997b..b1d7abde41c 100644
--- a/scripts/end-to-end-tests.js
+++ b/scripts/end-to-end-tests.js
@@ -69,6 +69,17 @@
     }),
   )
 
+  // Test resolving paths with a question mark (an invalid path on Windows)
+  tests.push(
+    test(['entry.js', '--bundle', '--outfile=node.js'], {
+      'entry.js': `
+        import x from "./file.js?ignore-me"
+        if (x !== 123) throw 'fail'
+      `,
+      'file.js': `export default 123`,
+    }),
+  )
+
   // Tests for symlinks
   //
   // Note: These are disabled on Windows because they fail when run with GitHub