diff --git a/externals/Makefile.am b/externals/Makefile.am
index 6da79ab8a9..7ae27dda39 100644
--- a/externals/Makefile.am
+++ b/externals/Makefile.am
@@ -34,12 +34,12 @@ endif
 
 # CWI ATerm
 
-ATERM = aterm-2.0.5
+ATERM = aterm-2.1
 
 $(ATERM).tar.gz:
 	@echo "Nix requires the CWI ATerm library to build."
-	@echo "Please download version 2.0.5 from"
-	@echo "  http://www.cwi.nl/projects/MetaEnv/aterm/aterm-2.0.5.tar.gz"
+	@echo "Please download version 2.1 from"
+	@echo "  http://www.cwi.nl/projects/MetaEnv/aterm/aterm-2.1.tar.gz"
 	@echo "and place it in the externals/ directory."
 	false