diff --git a/src/vtab/mod.rs b/src/vtab/mod.rs
index 2e7a11a..c4ae7b3 100644
--- a/src/vtab/mod.rs
+++ b/src/vtab/mod.rs
@@ -95,21 +95,13 @@ impl IndexInfo {
     }
 
     /// if `argv_index` > 0, constraint is part of argv to xFilter
-    pub fn set_argv_index(&mut self, constraint_idx: usize, argv_index: libc::c_int) {
-        unsafe {
-            let mut constraint_usages = slice::from_raw_parts_mut((*self.0).aConstraintUsage,
-                                                                  (*self.0).nConstraint as usize);
-            constraint_usages[constraint_idx].argvIndex = argv_index;
-        }
-    }
-    /// if `omit`, do not code a test for this constraint
-    pub fn set_omit(&mut self, constraint_idx: usize, omit: bool) {
-        unsafe {
-            let mut constraint_usages = slice::from_raw_parts_mut((*self.0).aConstraintUsage,
-                                                                  (*self.0).nConstraint as usize);
-            constraint_usages[constraint_idx].omit = if omit { 1 } else { 0 };
-        }
+    pub fn constraint_usage(&mut self, constraint_idx: usize) -> IndexConstraintUsage {
+        let mut constraint_usages = unsafe {
+            slice::from_raw_parts_mut((*self.0).aConstraintUsage, (*self.0).nConstraint as usize)
+        };
+        IndexConstraintUsage(&mut constraint_usages[constraint_idx])
     }
+
     /// Number used to identify the index
     pub fn set_idx_num(&mut self, idx_num: libc::c_int) {
         unsafe {
@@ -168,6 +160,19 @@ impl<'a> IndexConstraint<'a> {
     }
 }
 
+pub struct IndexConstraintUsage<'a>(&'a mut ffi::Struct_sqlite3_index_constraint_usage);
+
+impl<'a> IndexConstraintUsage<'a> {
+    /// if `argv_index` > 0, constraint is part of argv to xFilter
+    pub fn set_argv_index(&mut self, argv_index: libc::c_int) {
+        self.0.argvIndex = argv_index;
+    }
+    /// if `omit`, do not code a test for this constraint
+    pub fn set_omit(&mut self, omit: bool) {
+        self.0.omit = if omit { 1 } else { 0 };
+    }
+}
+
 /// Virtual table cursor trait.
 pub trait VTabCursor<V: VTab<Self>>: Sized {
     /// Accessor to the associated virtual table.
diff --git a/src/vtab/series.rs b/src/vtab/series.rs
index 9388abb..9dd526b 100644
--- a/src/vtab/series.rs
+++ b/src/vtab/series.rs
@@ -108,18 +108,21 @@ impl VTab<SeriesTabCursor> for SeriesTab {
         let mut num_of_arg = 0;
         if let Some(start_idx) = start_idx {
             num_of_arg += 1;
-            info.set_argv_index(start_idx, num_of_arg);
-            info.set_omit(start_idx, true);
+            let mut constraint_usage = info.constraint_usage(start_idx);
+            constraint_usage.set_argv_index(num_of_arg);
+            constraint_usage.set_omit(true);
         }
         if let Some(stop_idx) = stop_idx {
             num_of_arg += 1;
-            info.set_argv_index(stop_idx, num_of_arg);
-            info.set_omit(stop_idx, true);
+            let mut constraint_usage = info.constraint_usage(stop_idx);
+            constraint_usage.set_argv_index(num_of_arg);
+            constraint_usage.set_omit(true);
         }
         if let Some(step_idx) = step_idx {
             num_of_arg += 1;
-            info.set_argv_index(step_idx, num_of_arg);
-            info.set_omit(step_idx, true);
+            let mut constraint_usage = info.constraint_usage(step_idx);
+            constraint_usage.set_argv_index(num_of_arg);
+            constraint_usage.set_omit(true);
         }
         if idx_num.contains(BOTH) {
             // Both start= and stop= boundaries are available.