Index: src/func.c
==================================================================
--- src/func.c
+++ src/func.c
@@ -1528,11 +1528,11 @@
       p->rSum -= v;
       if( (p->approx|p->overflow)==0 && sqlite3AddInt64(&p->iSum, -1*v) ){
         p->overflow = 1;
       }
     }else{
-      p->rSum += sqlite3_value_double(argv[0]);
+      p->rSum -= sqlite3_value_double(argv[0]);
       p->approx = 1;
     }
   }
 }
 #else

Index: test/window6.test
==================================================================
--- test/window6.test
+++ test/window6.test
@@ -189,7 +189,25 @@
   WINDOW w AS (PARTITION BY "counter" ORDER BY "value" DESC) 
   ORDER BY "counter", RANK() OVER w
 } {
   1 20.0 1   1 10.0 2   2 3.0 1   2 1.0 2  3 100.0 1
 }
+
+do_execsql_test 8.2 {
+  SELECT "counter", "value", SUM("value") OVER 
+  (ORDER BY "id" ROWS 2 PRECEDING) 
+    FROM "sample" 
+  ORDER BY "id"
+} {
+  1 10.0 10.0   1 20.0 30.0   2 1.0 31.0   2 3.0 24.0   3 100.0 104.0
+}
+
+do_execsql_test 8.3 {
+  SELECT SUM("value") OVER 
+  (ORDER BY "id" ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) 
+    FROM "sample" 
+  ORDER BY "id"
+} {
+  10.0   30.0   31.0   24.0   104.0
+}
 
 finish_test