diff --git a/exercises/practice/grains/.meta/spec_generator.moon b/exercises/practice/grains/.meta/spec_generator.moon
index 31077ee..499e5a5 100644
--- a/exercises/practice/grains/.meta/spec_generator.moon
+++ b/exercises/practice/grains/.meta/spec_generator.moon
@@ -11,7 +11,12 @@ format = (number) ->
     else if case.property == 'square'
       table.insert lines, "assert.are.equal #{format case.expected}, Grains.#{case.property} #{case.input.square}"
     else
-      table.insert lines, "assert.are.equal #{format case.expected}, Grains.#{case.property}!"
+      -- apparently Lua can't represent this number exactly, so hardcode it.
+      --   > string.format('%.0f', 18446744073709551615)
+      --   18446744073709551616
+      --   > 18446744073709551615 == 18446744073709551616
+      --   true
+      table.insert lines, "assert.are.equal 18446744073709551615, Grains.#{case.property}!"
 
     table.concat [indent line, level for line in *lines], '\n'
 }
diff --git a/exercises/practice/grains/grains_spec.moon b/exercises/practice/grains/grains_spec.moon
index 712c3aa..df553ee 100644
--- a/exercises/practice/grains/grains_spec.moon
+++ b/exercises/practice/grains/grains_spec.moon
@@ -33,4 +33,4 @@ describe 'grains', ->
       assert.has.errors -> Grains.square 65, 'square must be between 1 and 64'
 
   pending 'returns the total number of grains on the board', ->
-    assert.are.equal 18446744073709551616, Grains.total!
+    assert.are.equal 18446744073709551615, Grains.total!