diff --git a/etc/config.csh/settings b/etc/config.csh/settings
index 76a30a8571..188c2fad5d 100644
--- a/etc/config.csh/settings
+++ b/etc/config.csh/settings
@@ -6,7 +6,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2016-2020 OpenCFD Ltd.
+#     Copyright (C) 2016-2021 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -174,12 +174,13 @@ _foamAddPath "${FOAM_USER_APPBIN}:${FOAM_SITE_APPBIN}:${FOAM_APPBIN}"
 # Dummy versions of external libraries. To be found last in library path
 _foamAddLib  "$FOAM_LIBBIN/dummy"
 
-# External (ThirdParty) libraries. Also allowed to be unset
-if ( -d "$WM_THIRD_PARTY_DIR" ) then
+# External (ThirdParty) libraries:
+# - check if already compiled, or will be compiled.
+#   can also be unset
+unsetenv FOAM_EXT_LIBBIN
+if ( -d "$WM_THIRD_PARTY_DIR/platforms" || -f "$WM_THIRD_PARTY_DIR/Allwmake" ) then
     setenv FOAM_EXT_LIBBIN "$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER$WM_PRECISION_OPTION$WM_LABEL_OPTION/lib"
     _foamAddLib "$FOAM_EXT_LIBBIN"
-else
-    unsetenv FOAM_EXT_LIBBIN
 endif
 
 # OpenFOAM libraries (user, group, standard)
diff --git a/etc/config.sh/settings b/etc/config.sh/settings
index f3a0d11137..16971ef0c1 100644
--- a/etc/config.sh/settings
+++ b/etc/config.sh/settings
@@ -6,7 +6,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2016-2020 OpenCFD Ltd.
+#     Copyright (C) 2016-2021 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -174,13 +174,14 @@ _foamAddPath "$FOAM_USER_APPBIN:$FOAM_SITE_APPBIN:$FOAM_APPBIN"
 # Dummy versions of external libraries. To be found last in library path
 _foamAddLib  "$FOAM_LIBBIN/dummy"
 
-# External (ThirdParty) libraries. Also allowed to be unset
-if [ -d "$WM_THIRD_PARTY_DIR" ]
+# External (ThirdParty) libraries:
+# - check if already compiled, or will be compiled.
+#   can also be unset
+unset FOAM_EXT_LIBBIN
+if [ -d "$WM_THIRD_PARTY_DIR/platforms" ] || [ -f "$WM_THIRD_PARTY_DIR/Allwmake" ]
 then
     export FOAM_EXT_LIBBIN="$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER$WM_PRECISION_OPTION$WM_LABEL_OPTION/lib"
     _foamAddLib "$FOAM_EXT_LIBBIN"
-else
-    unset FOAM_EXT_LIBBIN
 fi
 
 # OpenFOAM libraries (user, group, standard)