diff --git a/src/crypto/asn1.c b/src/crypto/asn1.c
index aca12bf30..9c71ffe10 100644
--- a/src/crypto/asn1.c
+++ b/src/crypto/asn1.c
@@ -81,18 +81,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define EINFO_ENOTTY_ALGORITHM \
 	__einfo_uniqify ( EINFO_ENOTTY, 0x01, "Inappropriate algorithm" )
 
-/**
- * Invalidate ASN.1 object cursor
- *
- * @v cursor		ASN.1 object cursor
- */
-void asn1_invalidate_cursor ( struct asn1_cursor *cursor ) {
-	static uint8_t asn1_invalid_object[] = { ASN1_END, 0 };
-
-	cursor->data = asn1_invalid_object;
-	cursor->len = 0;
-}
-
 /**
  * Start parsing ASN.1 object
  *
diff --git a/src/include/ipxe/asn1.h b/src/include/ipxe/asn1.h
index 5fbd58281..2e635b48a 100644
--- a/src/include/ipxe/asn1.h
+++ b/src/include/ipxe/asn1.h
@@ -314,15 +314,27 @@ struct asn1_bit_string {
 	unsigned int unused;
 } __attribute__ (( packed ));
 
+/**
+ * Invalidate ASN.1 object cursor
+ *
+ * @v cursor		ASN.1 object cursor
+ */
+static inline __attribute__ (( always_inline )) void
+asn1_invalidate_cursor ( struct asn1_cursor *cursor ) {
+	cursor->len = 0;
+}
+
 /**
  * Extract ASN.1 type
  *
  * @v cursor		ASN.1 object cursor
- * @ret type		Type
+ * @ret type		Type, or ASN1_END if cursor is invalid
  */
 static inline __attribute__ (( always_inline )) unsigned int
 asn1_type ( const struct asn1_cursor *cursor ) {
-	return ( *( ( const uint8_t * ) cursor->data ) );
+	const uint8_t *type = cursor->data;
+
+	return ( ( cursor->len >= sizeof ( *type ) ) ? *type : ASN1_END );
 }
 
 extern void asn1_invalidate_cursor ( struct asn1_cursor *cursor );