diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index e1e3537..54fd26b 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5077,20 +5077,20 @@
 
     RESET;
 
-    SUB_LAST; NEXT;                     // A0
+    /* Use 2^224 = P + 2^96 - 1 to modulo reduce the final carry */
+    SUB_LAST; NEXT;                     // A0 += -last_c
               NEXT;                     // A1
               NEXT;                     // A2
-    ADD_LAST; NEXT;                     // A3
+    ADD_LAST; NEXT;                     // A3 += last_c
               NEXT;                     // A4
               NEXT;                     // A5
                                         // A6
-
     RESET;
 
-    SUB_LAST; NEXT;                     // A0
+    SUB_LAST; NEXT;                     // A0 += -last_c
               NEXT;                     // A1
               NEXT;                     // A2
-    ADD_LAST; NEXT;                     // A3
+    ADD_LAST; NEXT;                     // A3 += last_c
               NEXT;                     // A4
               NEXT;                     // A5
                                         // A6