diff --git a/stim/envi/envi.h b/stim/envi/envi.h
index 5ebfa47..0ea815f 100644
--- a/stim/envi/envi.h
+++ b/stim/envi/envi.h
@@ -1200,7 +1200,7 @@ public:
 	/// @param x is the x-coordinate of the spectrum
 	/// @param y is the y-coordinate of the spectrum
 	template<typename T>
-	void spectrum(T* ptr, unsigned long long x, unsigned long long y, bool PROGRESS = false){
+	void spectrum(T* ptr, size_t x, size_t y, bool PROGRESS = false){
 
 		spectrum<T>(ptr, y * header.samples + x, PROGRESS);
 		/*void* temp = alloc_array<T>(header.bands);		//allocate space for the output array
diff --git a/stim/envi/envi_header.h b/stim/envi/envi_header.h
index 3b4fb4b..2555a26 100644
--- a/stim/envi/envi_header.h
+++ b/stim/envi/envi_header.h
@@ -24,10 +24,10 @@ struct envi_header
 
 	std::string description;
 
-	unsigned long long samples;	//x-axis
-	unsigned long long lines;		//y-axis
-	unsigned long long bands;		//spectral axis
-	unsigned long long header_offset;		//header offset for binary file (in bytes)
+	size_t samples;	//x-axis
+	size_t lines;		//y-axis
+	size_t bands;		//spectral axis
+	size_t header_offset;		//header offset for binary file (in bytes)
 	std::string file_type;			//should be "ENVI Standard"
 
 	envi_header::dataType data_type;			//data representation; common value is 4 (32-bit float)
--
libgit2 0.21.4