diff --git a/src/add-ons/kernel/drivers/network/pcnet/dev/pcn/Jamfile b/src/add-ons/kernel/drivers/network/pcnet/dev/pcn/Jamfile
index 5e73bd0a3a..c99ef08899 100644
--- a/src/add-ons/kernel/drivers/network/pcnet/dev/pcn/Jamfile
+++ b/src/add-ons/kernel/drivers/network/pcnet/dev/pcn/Jamfile
@@ -6,7 +6,7 @@ UseHeaders [ FDirName $(HAIKU_TOP) src libs compat freebsd_network compat ] : tr
 UsePrivateHeaders net system ;
 UsePrivateKernelHeaders ;
 
-SubDirCcFlags [ FDefines _KERNEL=1 FBSD_DRIVER=1 ] ;
+SubDirCcFlags [ FDefines _KERNEL=1 FBSD_DRIVER=1 _XOPEN_SOURCE ] ;
 
 KernelStaticLibrary pcnet_pcn.a
 	: