diff --git a/prism/ext/lp_solve_5.5_java/Makefile b/prism/ext/lp_solve_5.5_java/Makefile
index dd57738b..802d3a6e 100644
--- a/prism/ext/lp_solve_5.5_java/Makefile
+++ b/prism/ext/lp_solve_5.5_java/Makefile
@@ -11,7 +11,7 @@ all: checks lpsolve55java
 
 # Try and prevent accidental makes (i.e. called manually, not from top-level Makefile)
 checks:
-	@if [ "$(LIBPREFIX)" = "" ]; then \
+	@if [ "$(LIBSUFFIX)" = "" ]; then \
 	  (echo "Error: This Makefile is designed to be called from the main PRISM Makefile"; exit 1) \
 	fi; 
 
diff --git a/prism/ext/lpsolve55/Makefile b/prism/ext/lpsolve55/Makefile
index 35a4462c..2fddd551 100644
--- a/prism/ext/lpsolve55/Makefile
+++ b/prism/ext/lpsolve55/Makefile
@@ -22,7 +22,7 @@ all: checks ../../lib/$(LIBPREFIX)lpsolve55$(LIBSUFFIX)
 
 # Try and prevent accidental makes (i.e. called manually, not from top-level Makefile)
 checks:
-	@if [ "$(LIBPREFIX)" = "" ]; then \
+	@if [ "$(LIBSUFFIX)" = "" ]; then \
 	  (echo "Error: This Makefile is designed to be called from the main PRISM Makefile"; exit 1) \
 	fi;