diff --git a/skeletons/asn_internal.h b/skeletons/asn_internal.h
index 55e4e2b3b2cde7000b9a2d980682027cd00501dc..1de4ba9285dc7f917549386aa2b1ebb6f3ca6804 100644
--- a/skeletons/asn_internal.h
+++ b/skeletons/asn_internal.h
@@ -40,7 +40,7 @@ int get_asn1c_environment_version(void);	/* Run-time version */
 #define ASN_DEBUG_INDENT_ADD(i) do{}while(0)
 #else	/* !ASN_THREAD_SAFE */
 int asn_debug_indent;
-#define ASN_DEBUG_INDENT_ADD(i) do { asn_debug_indent += increment; } while(0)
+#define ASN_DEBUG_INDENT_ADD(i) do { asn_debug_indent += i; } while(0)
 #endif	/* ASN_THREAD_SAFE */
 #define	ASN_DEBUG(fmt, args...)	do {			\
 		int adi = asn_debug_indent;		\
diff --git a/skeletons/per_opentype.c b/skeletons/per_opentype.c
index 03a31d2d4afbef838298a83a7c52e4456d2131dd..a750fe80a79c17204dcbb65fc2893a93121605e2 100644
--- a/skeletons/per_opentype.c
+++ b/skeletons/per_opentype.c
@@ -7,6 +7,16 @@
 #include <constr_TYPE.h>
 #include <per_opentype.h>
 
+/* Thread safety requires sacrifice in output indentation. */
+#ifndef ASN_DEBUG_INDENT_ADD
+#ifdef  ASN_THREAD_SAFE
+#define ASN_DEBUG_INDENT_ADD(i) do{}while(0)
+#else   /* !ASN_THREAD_SAFE */
+int asn_debug_indent;
+#define ASN_DEBUG_INDENT_ADD(i) do { asn_debug_indent += i; } while(0)
+#endif  /* ASN_THREAD_SAFE */
+#endif  /* ASN_DEBUG_INDENT_ADD */
+
 typedef struct uper_ugot_key {
 	asn_per_data_t oldpd;	/* Old per data source */
 	size_t unclaimed;