diff --git a/build.sh b/build.sh
index 26fbfb2..58cacba 100755
--- a/build.sh
+++ b/build.sh
@@ -16,11 +16,34 @@
 # Contributor(s): 
 #
 
+# Make sure the value of JAVA_HOME is set
+if [ "x$JAVA_HOME" == "x" ]; then
+  echo "You must set the value of the JAVA_HOME environment variable."
+  exit 1
+fi
+
+# Make sure the value of TOMCAT_HOME is set
+if [ "x$TOMCAT_HOME" == "x" ]; then
+  echo "You must set the value of the TOMCAT_HOME environment variable."
+  exit 1
+fi
+
+# Make sure we can find the JAR files we need
+if [ ! -f $JAVA_HOME/lib/tools.jar ]; then
+  echo "Java tools JAR file (tools.jar) not found in $JAVA_HOME/lib."
+  exit 1
+fi
+if [ ! -f $TOMCAT_HOME/lib/ant.jar ]; then
+  echo "Ant JAR file (ant.jar) not found in $TOMCAT_HOME/lib."
+  exit 1
+fi
+if [ ! -f $TOMCAT_HOME/lib/servlet.jar ]; then
+  echo "Java Servlets JAR file (servlet.jar) not found in $TOMCAT_HOME/lib."
+  exit 1
+fi
+
 # Identify the custom class path components we need
-CP=$TOMCAT_HOME/lib/ant.jar:$TOMCAT_HOME/lib/servlet.jar
-CP=$CP:$TOMCAT_HOME/lib/jaxp.jar:$TOMCAT_HOME/lib/parser.jar
-CP=$CP:$JAVA_HOME/lib/tools.jar
+CP=$TOMCAT_HOME/lib/ant.jar:$TOMCAT_HOME/lib/servlet.jar:$JAVA_HOME/lib/tools.jar
 
 # Execute ANT to perform the requested build target
-java -classpath $CP:$CLASSPATH org.apache.tools.ant.Main \
-  -Dtomcat.home=$TOMCAT_HOME "$@"
+java -classpath $CP:$CLASSPATH org.apache.tools.ant.Main -Dtomcat.home=$TOMCAT_HOME "$@"