diff --git a/package/conntrack-tools/conntrack-tools.mk b/package/conntrack-tools/conntrack-tools.mk
index eac5841168..728758789c 100644
--- a/package/conntrack-tools/conntrack-tools.mk
+++ b/package/conntrack-tools/conntrack-tools.mk
@@ -13,10 +13,22 @@ CONNTRACK_TOOLS_DEPENDENCIES = host-pkgconf \
 CONNTRACK_TOOLS_LICENSE = GPLv2+
 CONNTRACK_TOOLS_LICENSE_FILES = COPYING
 
+CONNTRACK_TOOLS_CFLAGS = $(TARGET_CFLAGS)
+
+# Some of conntrack-tools source files include both linux/in.h (via
+# linux/netfilter.h for kernel headers >= 4.2) and netinet/in.h, which
+# causes some symbol conflicts when musl is used. Defining __GLIBC__
+# works around that issue since the kernel headers are prepared to
+# avoid redefinition of certain symbols when they see __GLIBC__.
+ifeq ($(BR2_TOOLCHAIN_USES_MUSL),y)
+CONNTRACK_TOOLS_CFLAGS += -D__GLIBC__
+endif
+
 ifeq ($(BR2_PACKAGE_LIBTIRPC),y)
-CONNTRACK_TOOLS_CONF_ENV += \
-	CFLAGS="$(TARGET_CFLAGS) `$(PKG_CONFIG_HOST_BINARY) --cflags libtirpc`"
+CONNTRACK_TOOLS_CFLAGS += `$(PKG_CONFIG_HOST_BINARY) --cflags libtirpc`
 CONNTRACK_TOOLS_DEPENDENCIES += libtirpc host-pkgconf
 endif
 
+CONNTRACK_TOOLS_CONF_ENV = CFLAGS="$(CONNTRACK_TOOLS_CFLAGS)"
+
 $(eval $(autotools-package))