diff --git a/config/default.mk b/config/default.mk
index 29db81a2a27a66b03d3e469f8485dd175ae9943f..fd84d5f2d08834986158a929e4d649ce91fb36da 100644
--- a/config/default.mk
+++ b/config/default.mk
@@ -1,3 +1,10 @@
+# Boolean flag which defines this FSL installation
+# as being from FSL 6.0.6 or newer (a conda-based
+# FSL installation). This flag may be used by FSL
+# Makefiles which need to preserve support for
+# older versions of FSL.
+FSL_POST_606 := true
+
 # Platform specific settings and defaults,
 # which are used by vars.mk
 include ${FSLCONFDIR}/buildSettings.mk