diff --git a/include/qpdf/QPDFExc.hh b/include/qpdf/QPDFExc.hh
index c0a0598..11e6cfe 100644
--- a/include/qpdf/QPDFExc.hh
+++ b/include/qpdf/QPDFExc.hh
@@ -12,6 +12,7 @@
 #include <qpdf/Types.h>
 
 #include <qpdf/Constants.h>
+#include <string>
 #include <stdexcept>
 
 class QPDFExc: public std::runtime_error