diff --git a/cSpell.json b/cSpell.json
index 9a4eea8..1fd8966 100644
--- a/cSpell.json
+++ b/cSpell.json
@@ -630,7 +630,7 @@
     "submatches",
     "subparsers",
     "subramanyam",
-    "subtract",
+    "substract",
     "swversion",
     "sysnow",
     "sysroot",
diff --git a/include/qpdf/QIntC.hh b/include/qpdf/QIntC.hh
index 6e997ff..8db0a89 100644
--- a/include/qpdf/QIntC.hh
+++ b/include/qpdf/QIntC.hh
@@ -277,7 +277,7 @@ namespace QIntC // QIntC = qpdf Integer Conversion
         QIntC::range_check_error<T>(cur, delta);
     }
 
-    // ABI: fix spelling error in function name
+    // ABI: fix spelling error in function name. Also remove "substract" from spelling dictionary.
     template <typename T>
     void
     range_check_substract_error(T const& cur, T const& delta)