diff --git a/bin/named/main.c b/bin/named/main.c
index 2201ce002d..c66425e18f 100644
--- a/bin/named/main.c
+++ b/bin/named/main.c
@@ -1524,15 +1524,6 @@ main(int argc, char *argv[]) {
 	pk11_result_register();
 #endif /* if USE_PKCS11 */
 
-#if !ISC_MEM_DEFAULTFILL
-	/*
-	 * Update the default flags to remove ISC_MEMFLAG_FILL
-	 * before we parse the command line. If disabled here,
-	 * it can be turned back on with -M fill.
-	 */
-	isc_mem_defaultflags &= ~ISC_MEMFLAG_FILL;
-#endif /* if !ISC_MEM_DEFAULTFILL */
-
 	parse_command_line(argc, argv);
 
 #ifdef ENABLE_AFL
diff --git a/configure.ac b/configure.ac
index c8d75b2bf7..1d1d1c7fa6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -158,7 +158,7 @@ AC_ARG_ENABLE([developer],
 
 AS_IF([test "$enable_developer" = "yes"],
       [DEVELOPER_MODE=yes
-       STD_CPPFLAGS="$STD_CPPFLAGS -DISC_MEM_DEFAULTFILL=1 -DISC_LIST_CHECKINIT=1"
+       STD_CPPFLAGS="$STD_CPPFLAGS -DISC_MEM_DEFAULTFILL=1 -DISC_MEM_TRACKLINES=1 -DISC_LIST_CHECKINIT=1"
        test "${enable_fixed_rrset+set}" = set || enable_fixed_rrset=yes
        test "${enable_querytrace+set}" = set || enable_querytrace=yes
        test "${with_cmocka+set}" = set || with_cmocka=yes
diff --git a/lib/isc/include/isc/mem.h b/lib/isc/include/isc/mem.h
index 7d63ffef23..1d274316dd 100644
--- a/lib/isc/include/isc/mem.h
+++ b/lib/isc/include/isc/mem.h
@@ -33,7 +33,7 @@ typedef void (*isc_mem_water_t)(void *, int);
  * allocation and freeing by file and line number.
  */
 #ifndef ISC_MEM_TRACKLINES
-#define ISC_MEM_TRACKLINES 1
+#define ISC_MEM_TRACKLINES 0
 #endif /* ifndef ISC_MEM_TRACKLINES */
 
 LIBISC_EXTERNAL_DATA extern unsigned int isc_mem_debugging;
@@ -90,10 +90,14 @@ LIBISC_EXTERNAL_DATA extern unsigned int isc_mem_defaultflags;
 #define ISC_MEMFLAG_FILL \
 	0x00000004 /* fill with pattern after alloc and frees */
 
-#if !ISC_MEM_USE_INTERNAL_MALLOC
-#define ISC_MEMFLAG_DEFAULT 0
-#else /* if !ISC_MEM_USE_INTERNAL_MALLOC */
+/*%
+ * Define ISC_MEM_DEFAULTFILL=1 to turn filling the memory with pattern
+ * after alloc and free.
+ */
+#if ISC_MEM_DEFAULTFILL
 #define ISC_MEMFLAG_DEFAULT ISC_MEMFLAG_FILL
+#else /* if !ISC_MEM_USE_INTERNAL_MALLOC */
+#define ISC_MEMFLAG_DEFAULT 0
 #endif /* if !ISC_MEM_USE_INTERNAL_MALLOC */
 
 /*%