diff --git a/docx.go b/docx.go
index 185e52d..dd27aa4 100644
--- a/docx.go
+++ b/docx.go
@@ -62,7 +62,13 @@ func ConvertDocx(r io.Reader) (string, map[string]string, error) {
 	meta := make(map[string]string)
 	var textHeader, textBody, textFooter string
 	for _, override := range contentTypeDefinition.Overrides {
-		f := zipFiles[override.PartName]
+		f, ok := zipFiles[override.PartName]
+		if !ok {
+			// Some docx files declare overrides for parts that are not
+			// present in the archive. Skip them rather than dereferencing
+			// a nil *zip.File and panicking.
+			continue
+		}
 
 		switch {
 		case override.ContentType == "application/vnd.openxmlformats-package.core-properties+xml":