diff --git a/lib/asn1/gen.c b/lib/asn1/gen.c
index 39ea9d037..84d31a859 100644
--- a/lib/asn1/gen.c
+++ b/lib/asn1/gen.c
@@ -273,6 +273,11 @@ init_generate (const char *filename, const char *base)
 	  "#define ASN1CALL\n"
 	  "#endif\n",
 	  headerfile);
+    fputs("#ifndef ENOTSUP\n"
+	  "/* Very old MSVC CRTs lack ENOTSUP */\n"
+	  "#define ENOTSUP EINVAL\n"
+	  "#endif\n",
+	  headerfile);
     fprintf (headerfile, "struct units;\n\n");
     fprintf (headerfile, "#endif\n\n");
     if (asprintf(&fn, "%s_files", base) < 0 || fn == NULL)
diff --git a/lib/asn1/gen_print.c b/lib/asn1/gen_print.c
index 5ff2da9b1..4cca9e044 100644
--- a/lib/asn1/gen_print.c
+++ b/lib/asn1/gen_print.c
@@ -38,6 +38,6 @@ generate_type_print_stub(const Symbol *s)
 {
     fprintf(codefile, "char * ASN1CALL\n"
 	    "print_%s(const %s *data, int flags)\n"
-	    "{ errno = ENOTSUP; return 0; }\n\n",
+	    "{ errno = EINVAL; return 0; }\n\n",
 	    s->gen_name, s->gen_name);
 }
diff --git a/lib/asn1/template.c b/lib/asn1/template.c
index 27f4300ee..cd6125241 100644
--- a/lib/asn1/template.c
+++ b/lib/asn1/template.c
@@ -38,6 +38,11 @@
 #include <vis.h>
 #include <vis-extras.h>
 
+#ifndef ENOTSUP
+/* Very old MSVC CRTs don't have ENOTSUP */
+#define ENOTSUP EINVAL
+#endif
+
 struct asn1_type_func asn1_template_prim[A1T_NUM_ENTRY] = {
 #define el(name, type) {				\
 	(asn1_type_encode)der_put_##name,		\