diff --git a/libcxx/test/std/input.output/iostream.format/input.streams/istream.formatted/istream_extractors/streambuf.pass.cpp b/libcxx/test/std/input.output/iostream.format/input.streams/istream.formatted/istream_extractors/streambuf.pass.cpp
index ccd043cc9607..5afc56d8aaaa 100644
--- a/libcxx/test/std/input.output/iostream.format/input.streams/istream.formatted/istream_extractors/streambuf.pass.cpp
+++ b/libcxx/test/std/input.output/iostream.format/input.streams/istream.formatted/istream_extractors/streambuf.pass.cpp
@@ -50,7 +50,7 @@ protected:
                 str_.resize(str_.capacity());
                 base::setp(const_cast<CharT*>(str_.data()),
                            const_cast<CharT*>(str_.data() + str_.size()));
-                base::pbump(n+1);
+                base::pbump(static_cast<int>(n+1));
             }
             return ch;
         }