diff --git a/Cargo.lock b/Cargo.lock
index 54c475f..3751de2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -642,6 +642,7 @@ dependencies = [
  "libdeflater",
  "log",
  "lru",
+ "ndarray 0.15.6",
  "ndarray 0.16.0",
  "netcdf",
  "numpy",
@@ -998,6 +999,7 @@ dependencies = [
  "num-integer",
  "num-traits",
  "rawpointer",
+ "rayon",
 ]
 
 [[package]]
diff --git a/Cargo.toml b/Cargo.toml
index 942f5a4..e1bf2a3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,6 +36,8 @@ hdf5-sys = { package = "hdf5-metno-sys", version = "0.9.1" }
 log = "0.4"
 rayon = "1.10"
 ndarray = { version = "0.16", features = [ "rayon" ] }
+# Remove when https://github.com/PyO3/rust-numpy/pull/439 is addressed
+ndarray_0_15 = { package = "ndarray", version = "0.15", features = ["rayon"] }
 pyo3 = { version = "0.21", optional = true, features = ["anyhow", "auto-initialize", "abi3-py39"] }
 numpy = { version = "0.21.0", optional = true }
 netcdf = { version = "0.10.4", optional = true }
diff --git a/src/python/mod.rs b/src/python/mod.rs
index c5847f4..430cb1b 100644
--- a/src/python/mod.rs
+++ b/src/python/mod.rs
@@ -164,7 +164,7 @@ impl Dataset {
         let arr = arr.downcast::<PyArrayDyn<T>>().unwrap();
 
         let mut v = unsafe { arr.as_array_mut() };
-        v.mapv_inplace(|v| if v == cond { fv } else { v });
+        v.par_mapv_inplace(|v| if v == cond { fv } else { v });
     }
 }