diff --git a/lib/glossary_macros.rb b/lib/glossary_macros.rb
index 9d28753..b1a6f88 100644
--- a/lib/glossary_macros.rb
+++ b/lib/glossary_macros.rb
@@ -4,15 +4,33 @@ module GlossaryMacros
 
     desc "create macro which links to glossary term by id."
     macro :termno do |obj, args|
-      term_id = args.first
-      term = GlossaryTerm.find(term_id)
-      link_to term.name, project_glossary_term_path(@project, term)
+      begin
+        raise 'no parameters' if args.count.zero?
+        raise 'too many parameters' if args.count > 1
+        term_id = args.first
+        term = GlossaryTerm.find(term_id)
+        link_to term.name, project_glossary_term_path(@project, term)
+      rescue => err_msg
+        raise <<-TEXT.html_safe
+Parameter error: #{err_msg}<br>
+Usage: {{termno(glossary_term_id)}}
+TEXT
+      end
     end
 
     desc "create macro which links to glossary term by name."
     macro :term do |obj, args|
-      term = GlossaryTerm.find_by(name: args.first)
-      link_to term.name, project_glossary_term_path(@project, term)
+      begin
+        raise 'no parameters' if args.count.zero?
+        raise 'too many parameters' if args.count > 1
+        term = GlossaryTerm.find_by!(name: args.first)
+        link_to term.name, project_glossary_term_path(@project, term)
+      rescue => err_msg
+        raise <<-TEXT.html_safe
+Parameter error: #{err_msg}<br>
+Usage: {{term(name)}}
+TEXT
+      end
     end
 
   end