diff --git a/bin/varnishd/cache/cache_vrt_vmod.c b/bin/varnishd/cache/cache_vrt_vmod.c
index 65e707480cf..719df9f5064 100644
--- a/bin/varnishd/cache/cache_vrt_vmod.c
+++ b/bin/varnishd/cache/cache_vrt_vmod.c
@@ -38,6 +38,7 @@
 #include <stdlib.h>
 
 #include "vcli_serve.h"
+#include "vmod_abi.h"
 #include "vrt.h"
 
 /*--------------------------------------------------------------------
@@ -65,6 +66,16 @@ struct vmod {
 
 static VTAILQ_HEAD(,vmod)	vmods = VTAILQ_HEAD_INITIALIZER(vmods);
 
+static unsigned
+vmod_abi_mismatch(const struct vmod_data *d)
+{
+
+	if (d->vrt_major == 0 && d->vrt_minor == 0)
+		return (d->abi == NULL || strcmp(d->abi, VMOD_ABI_Version));
+
+	return (d->vrt_major != VRT_MAJOR_VERSION ||
+	    d->vrt_minor > VRT_MINOR_VERSION);
+}
 
 int
 VRT_Vmod_Init(VRT_CTX, struct vmod **hdl, void *ptr, int len, const char *nm,
@@ -112,15 +123,13 @@ VRT_Vmod_Init(VRT_CTX, struct vmod **hdl, void *ptr, int len, const char *nm,
 			FREE_OBJ(v);
 			return (1);
 		}
-		if (d->vrt_major != VRT_MAJOR_VERSION ||
-		    d->vrt_minor > VRT_MINOR_VERSION ||
+		if (vmod_abi_mismatch(d) ||
 		    d->name == NULL ||
 		    strcmp(d->name, nm) ||
 		    d->func == NULL ||
 		    d->func_len <= 0 ||
 		    d->proto == NULL ||
-		    d->spec == NULL ||
-		    d->abi == NULL) {
+		    d->spec == NULL) {
 			VSB_printf(ctx->msg,
 			    "Loading VMOD %s from %s:\n", nm, path);
 			VSB_printf(ctx->msg, "VMOD data is mangled.\n");
diff --git a/config.phk b/config.phk
index 7356757453c..b54257a8fec 100644
--- a/config.phk
+++ b/config.phk
@@ -107,25 +107,23 @@ fi
 
 VCSF=include/vcs_version.h
 VMAV=include/vmod_abi.h
+V=NOGIT
 
 if [ -d ./.git ] ; then
 	V=`git show -s --pretty=format:%h`
-	B=`git rev-parse --abbrev-ref HEAD`
-else
-	V="NOGIT"
-	B="NOGIT"
 fi
-(
-echo "/* $V */"
-echo "/*"
-echo " * NB:  This file is machine generated, DO NOT EDIT!"
-echo " *"
-echo " * make(1) updates this when necessary"
-echo " *"
-echo " */"
-echo "#define VCS_Version \"$V\""
-echo "#define VCS_Branch \"$B\""
-) > ${VCSF}_
+
+cat > ${VCSF}_ <<EOF
+/* $V */
+/*
+ * NB:  This file is machine generated, DO NOT EDIT!
+ *
+ * make(1) updates this when necessary
+ *
+ */
+#define VCS_Version "$V"
+EOF
+
 if [ ! -f ${VCSF} ] ; then
 	mv ${VCSF}_ ${VCSF}
 	rm -f ${VMAV}
diff --git a/lib/libvcc/generate.py b/lib/libvcc/generate.py
index ed31ae90aa3..7365d98e2ec 100755
--- a/lib/libvcc/generate.py
+++ b/lib/libvcc/generate.py
@@ -1417,7 +1417,6 @@ def rst_where(fo, h, l):
 	fo = open(vcsfn, "w")
 	file_header(fo)
 	fo.write('#define VCS_Version "%s"\n' % v)
-	fo.write('#define VCS_Branch "%s"\n' % b)
 	fo.close()
 
 	for i in open(os.path.join(buildroot, "Makefile")):
diff --git a/lib/libvcc/vcc_vmod.c b/lib/libvcc/vcc_vmod.c
index d46e4962984..06ca562f694 100644
--- a/lib/libvcc/vcc_vmod.c
+++ b/lib/libvcc/vcc_vmod.c
@@ -155,7 +155,7 @@ vcc_ParseImport(struct vcc *tl)
 		vcc_ErrWhere(tl, mod);
 		return;
 	}
-	if (strcmp(VCS_Branch, "master") == 0 &&
+	if (vmd->vrt_major == 0 && vmd->vrt_minor == 0 &&
 	    strcmp(vmd->abi, VMOD_ABI_Version) != 0) {
 		VSB_printf(tl->sb, "Incompatible VMOD %.*s\n", PF(mod));
 		VSB_printf(tl->sb, "\tFile name: %s\n", fnp);
@@ -164,8 +164,8 @@ vcc_ParseImport(struct vcc *tl)
 		vcc_ErrWhere(tl, mod);
 		return;
 	}
-	if (vmd->vrt_major != VRT_MAJOR_VERSION ||
-	    vmd->vrt_minor > VRT_MINOR_VERSION) {
+	if (vmd->vrt_major != 0 && (vmd->vrt_major != VRT_MAJOR_VERSION ||
+	    vmd->vrt_minor > VRT_MINOR_VERSION)) {
 		VSB_printf(tl->sb, "Incompatible VMOD %.*s\n", PF(mod));
 		VSB_printf(tl->sb, "\tFile name: %s\n", fnp);
 		VSB_printf(tl->sb, "\tVMOD version %u.%u\n",
diff --git a/lib/libvcc/vmodtool.py b/lib/libvcc/vmodtool.py
index 90b888eb5b0..ab78cff023d 100755
--- a/lib/libvcc/vmodtool.py
+++ b/lib/libvcc/vmodtool.py
@@ -44,6 +44,7 @@
 import random
 
 rstfmt = False
+strict_abi = True
 
 ctypes = {
 	'ACL':		"VCL_ACL",
@@ -434,6 +435,13 @@ def rsttail(self, fo, man):
 			fo.write("* :ref:`%s`\n" % i[1])
 		fo.write("\n")
 
+class s_abi(stanza):
+	def parse(self):
+		if self.line[1] not in ('strict', 'vrt'):
+			err("Valid ABI types are 'strict' or 'vrt', got '%s'\n" %
+			    self.line[1])
+		strict_abi = self.line[1] == 'strict'
+
 class s_event(stanza):
 	def parse(self):
 		self.event_func = self.line[1]
@@ -651,6 +659,8 @@ def parse(self):
 					err("$Module must be first stanze")
 			if c[0] == "Module":
 				s_module(c, b[1:], self)
+			elif c[0] == "ABI":
+				s_abi(c, b[1:], self)
 			elif c[0] == "Event":
 				s_event(c, b[1:], self)
 			elif c[0] == "Function":
@@ -734,8 +744,12 @@ def api(self, fo):
 			fo.write("\n/*lint -esym(%d, Vmod_%s_Data) */\n" % (i, self.modname))
 		fo.write("const struct vmod_data Vmod_%s_Data = {\n" %
 		    self.modname)
-		fo.write("\t.vrt_major =\tVRT_MAJOR_VERSION,\n")
-		fo.write("\t.vrt_minor =\tVRT_MINOR_VERSION,\n")
+		if strict_abi:
+			fo.write("\t.vrt_major =\t0,\n")
+			fo.write("\t.vrt_minor =\t0,\n")
+		else:
+			fo.write("\t.vrt_major =\tVRT_MAJOR_VERSION,\n")
+			fo.write("\t.vrt_minor =\tVRT_MINOR_VERSION,\n")
 		fo.write('\t.name =\t\t"%s",\n' % self.modname)
 		fo.write('\t.func =\t\t&Vmod_Func,\n')
 		fo.write('\t.func_len =\tsizeof(Vmod_Func),\n')
diff --git a/lib/libvmod_debug/vmod.vcc b/lib/libvmod_debug/vmod.vcc
index 93234886256..1b7889d9bdb 100644
--- a/lib/libvmod_debug/vmod.vcc
+++ b/lib/libvmod_debug/vmod.vcc
@@ -26,6 +26,7 @@
 # SUCH DAMAGE.
 
 $Module debug 3 Development, test and debug
+$ABI strict
 
 DESCRIPTION
 ===========
diff --git a/lib/libvmod_directors/vmod.vcc b/lib/libvmod_directors/vmod.vcc
index cce8acb25ab..9282ba35061 100644
--- a/lib/libvmod_directors/vmod.vcc
+++ b/lib/libvmod_directors/vmod.vcc
@@ -33,6 +33,7 @@
 # SUCH DAMAGE.
 
 $Module directors 3 Varnish Directors Module
+$ABI strict
 
 DESCRIPTION
 ===========
diff --git a/lib/libvmod_std/vmod.vcc b/lib/libvmod_std/vmod.vcc
index 0923fb7203a..c98eb262d76 100644
--- a/lib/libvmod_std/vmod.vcc
+++ b/lib/libvmod_std/vmod.vcc
@@ -26,6 +26,7 @@
 # SUCH DAMAGE.
 
 $Module std 3 Varnish Standard Module
+$ABI strict
 
 DESCRIPTION
 ===========