diff --git a/package/libpcap/libpcap.mk b/package/libpcap/libpcap.mk
index 81e7cd4ab0..24215ebed5 100644
--- a/package/libpcap/libpcap.mk
+++ b/package/libpcap/libpcap.mk
@@ -12,8 +12,11 @@ LIBPCAP_CPE_ID_VENDOR = tcpdump
 LIBPCAP_INSTALL_STAGING = YES
 LIBPCAP_DEPENDENCIES = host-flex host-bison host-pkgconf
 
+# ac_cv_prog_cc_c99 is required for BR2_USE_WCHAR=n because the C99 test
+# provided by autoconf relies on wchar_t.
 LIBPCAP_CONF_ENV = \
 	ac_cv_header_linux_wireless_h=yes \
+	ac_cv_prog_cc_c99=-std=gnu99 \
 	CFLAGS="$(LIBPCAP_CFLAGS)"
 LIBPCAP_CFLAGS = $(TARGET_CFLAGS)
 LIBPCAP_CONF_OPTS = --disable-yydebug --with-pcap=linux --without-dag \