diff --git a/stim/envi/hsi.h b/stim/envi/hsi.h
index 71c84c5..43ad653 100644
--- a/stim/envi/hsi.h
+++ b/stim/envi/hsi.h
@@ -128,14 +128,14 @@ public:
 
 	/// Get the list of band numbers that bound a list of wavelengths
 	void band_bounds(std::vector<double> wavelengths,
-		std::vector<unsigned long long>& low_bands,
-		std::vector<unsigned long long>& high_bands) {
+		std::vector<size_t>& low_bands,
+		std::vector<size_t>& high_bands) {
 
 		unsigned long long W = w.size();									//get the number of wavelengths in the list
 		low_bands.resize(W);												//pre-allocate space for the band lists
 		high_bands.resize(W);
 
-		for (unsigned long long wl = 0; wl < W; wl++) {						//for each wavelength
+		for (size_t wl = 0; wl < W; wl++) {						//for each wavelength
 			band_bounds(wavelengths[wl], low_bands[wl], high_bands[wl]);	//find the low and high bands
 		}
 	}
--
libgit2 0.21.4