diff --git a/pineappl/src/grid.rs b/pineappl/src/grid.rs
index b9cfc6f6..c0b7b77f 100644
--- a/pineappl/src/grid.rs
+++ b/pineappl/src/grid.rs
@@ -1531,46 +1531,6 @@ impl Grid {
             })
             .collect();
 
-        // the x1 and x2 grid values are the same across all non-zero subgrids
-        let first_non_zero_grid = self
-            .subgrids
-            .iter()
-            .find(|subgrid| !subgrid.is_empty())
-            .unwrap_or_else(|| unreachable!());
-        // source x1/x2 grid might differ and be differently sorted than the operator
-        let x1_grid = if has_pdf1 {
-            first_non_zero_grid
-                .x1_grid()
-                .iter()
-                .map(|x| {
-                    eko_info
-                        .grid_axes
-                        .x_grid
-                        .iter()
-                        .position(|xi| approx_eq!(f64, *xi, *x, ulps = 64))
-                        .unwrap_or_else(|| unreachable!())
-                })
-                .collect()
-        } else {
-            Vec::new()
-        };
-        let x2_grid = if has_pdf2 {
-            first_non_zero_grid
-                .x2_grid()
-                .iter()
-                .map(|x| {
-                    eko_info
-                        .grid_axes
-                        .x_grid
-                        .iter()
-                        .position(|xi| approx_eq!(f64, *xi, *x, ulps = 64))
-                        .unwrap_or_else(|| unreachable!())
-                })
-                .collect()
-        } else {
-            Vec::new()
-        };
-
         // iterate over all bins, which are mapped one-to-one from the target to the source grid
         for bin in 0..self.bin_info().bins() {
             // iterate over the source grid luminosities
@@ -1619,6 +1579,40 @@ impl Grid {
 
                     let src_subgrid = &self.subgrids[[order, bin, src_lumi]];
 
+                    // source x1/x2 grid might differ and be differently sorted than the operator
+                    let x1_grid = if has_pdf1 {
+                        src_subgrid
+                            .x1_grid()
+                            .iter()
+                            .map(|x| {
+                                eko_info
+                                    .grid_axes
+                                    .x_grid
+                                    .iter()
+                                    .position(|xi| approx_eq!(f64, *xi, *x, ulps = 64))
+                                    .unwrap_or_else(|| unreachable!())
+                            })
+                            .collect()
+                    } else {
+                        Vec::new()
+                    };
+                    let x2_grid = if has_pdf2 {
+                        src_subgrid
+                            .x2_grid()
+                            .iter()
+                            .map(|x| {
+                                eko_info
+                                    .grid_axes
+                                    .x_grid
+                                    .iter()
+                                    .position(|xi| approx_eq!(f64, *xi, *x, ulps = 64))
+                                    .unwrap_or_else(|| unreachable!())
+                            })
+                            .collect()
+                    } else {
+                        Vec::new()
+                    };
+
                     for ((iq2, ix1, ix2), &value) in src_subgrid.iter() {
                         let scale = src_subgrid.mu2_grid()[iq2].fac;
                         let src_iq2 = src_array_q2_grid