diff --git a/ext/CrystallinePyPlotExt.jl b/ext/CrystallinePyPlotExt.jl
index 64c0f3c0..c08694c9 100644
--- a/ext/CrystallinePyPlotExt.jl
+++ b/ext/CrystallinePyPlotExt.jl
@@ -13,6 +13,8 @@ else
 end
 using Crystalline
 using Crystalline: AbstractFourierLattice, AbstractVec, calcfouriergridded
+ # extend rather than define so it can be called externally via `Crystalline.(...)`
+import Crystalline: _create_isosurf_plot_data
 
 using Meshing: MarchingCubes, isosurface
 using Statistics: quantile
diff --git a/src/Crystalline.jl b/src/Crystalline.jl
index e94ced90..8d3595e2 100644
--- a/src/Crystalline.jl
+++ b/src/Crystalline.jl
@@ -175,6 +175,9 @@ export position, inv, isapprox
 if !isdefined(Base, :get_extension)
     using Requires # load extensions via Requires.jl on Julia versions <v1.9
 end
+# define functions we want to extend and have accessible via `Crystalline.(...)` if an
+# extension is loaded
+function _create_isosurf_plot_data end # implemented on CrystallinePyPlotExt load
 
 ## __init__
 # - open .jld2 data files, so we don't need to keep opening/closing them