diff --git a/calculus.tex b/calculus.tex
index 7a69f8a..93aca94 100644
--- a/calculus.tex
+++ b/calculus.tex
@@ -4327,7 +4327,7 @@ interpretation. Mathematics is not really concerned with these
 interpretation; mathematics is concerned with definitions and theorems,
 but I don't mean mathematicians. I believe that mathematicians are very
 much concerned with these interpretations, but ``negative area'' is not
-problem for a mathematician. If a negative balance in your account if
+problem for a mathematician. If a negative balance in your account is
 money that you owe, then a negative area is an area that you don't have.
 
 We talk about these arbitrary points in the definition because they are