diff --git a/src/grids.jl b/src/grids.jl
index 65bea90..d93afc5 100644
--- a/src/grids.jl
+++ b/src/grids.jl
@@ -19,18 +19,22 @@ Interpolated value in the grid that convert `Datumₛ` to `Datumₜ`
 of the coordinate with latitude `lat` and longitude `lon`.
 """
 function interpolatelatlon(Datumₛ, Datumₜ, lat, lon)
-  lat′ = ustrip(lat)
-  lon′ = ustrip(lon)
   interps = interpolators(Datumₛ, Datumₜ)
-  for interp in interps
+  _interpolatelatlon(interps, ustrip(lat), ustrip(lon))
+end
+
+function _interpolatelatlon(interps::AbstractVector, lat, lon)
+  @inbounds for interp in interps
     (lonmin, lonmax), (latmin, latmax) = bounds(interp)
-    if lonmin < lon′ < lonmax && latmin < lat′ < latmax
-      return interp(lon′, lat′)
+    if lonmin < lon < lonmax && latmin < lat < latmax
+      return interp(lon, lat)
     end
   end
   throw(ArgumentError("coordinates outside of the transform domain"))
 end
 
+_interpolatelatlon(interp, lat, lon) = interp(lon, lat)
+
 """
     interpolators(Datumₛ, Datumₜ)
 
@@ -50,7 +54,7 @@ function interpolators(Datumₛ, Datumₜ)
   interps = if geotiff isa GeoTIFF.GeoTIFFImageIterator
     map(interpolator, geotiff)
   else
-    [interpolator(geotiff)]
+    interpolator(geotiff)
   end
 
   # store interpolators in cache
diff --git a/test/converions.jl b/test/converions.jl
index 9274391..fe779e4 100644
--- a/test/converions.jl
+++ b/test/converions.jl
@@ -264,6 +264,6 @@
   @test allapprox(c3, c1)
 
   # error: coordinates outside of the transform domain
-  c1 = LatLon{SAD96}(T(10), T(-10))
-  @test_throws ArgumentError convert(LatLon{SIRGAS2000}, c1)
+  c1 = LatLon{RD83}(T(65), T(25))
+  @test_throws ArgumentError convert(LatLon{ETRFLatest}, c1)
 end