diff --git a/stim/envi/envi.h b/stim/envi/envi.h
index a19652a..2fc2fe7 100644
--- a/stim/envi/envi.h
+++ b/stim/envi/envi.h
@@ -7,6 +7,7 @@
 #include "../envi/bil.h"
 #include "../math/fd_coefficients.h"
 #include <stim/parser/filename.h>
+#include <stim/util/filesize.h>
 #include <iostream>
 #include <fstream>
 //#include "../image/image.h"
@@ -83,22 +84,8 @@ public:
 		return true;
 	}
 
-	static size_t file_size(std::string filename){
-		FILE *p_file = NULL;
-		p_file = fopen(filename.c_str(),"rb");
-		if(!p_file){
-			std::cout<<"ERROR: could not open "<<filename<<std::endl;
-			exit(1);
-		}
-		fseek(p_file,0,SEEK_END);
-		size_t size = ftell(p_file);
-		fclose(p_file);
-		return size;
-	}
-
 	//test to determine if the specified file is an ENVI file
 	static bool is_envi(std::string fname, std::string hname = ""){
-		return true;
 		stim::filename data_file(fname);
 		stim::filename header_file;
 		if(hname == ""){								//if the header isn't provided
@@ -111,10 +98,7 @@ public:
 		if(H.load(header_file) == false)				//load the header file, if it doesn't load return false
 			return false;
 		size_t targetBytes = H.data_bytes();			//get the number of bytes that SHOULD be in the data file
-		//std::ifstream infile(data_file.str(), std::ifstream::binary);			//load the data file
-		//if(!infile) return false;						//if the data file doesn't load, return false
-		//size_t bytes = infile.tellg();					//get the number of actual bytes in the file
-		size_t bytes = file_size(fname);
+		size_t bytes = stim::file_size(fname);
 		if(bytes != targetBytes) return false;			//if the data doesn't match the header, return false
 		return true;									//otherwise everything looks fine
 
diff --git a/stim/util/filesize.h b/stim/util/filesize.h
new file mode 100644
index 0000000..273fe8b
--- /dev/null
+++ b/stim/util/filesize.h
@@ -0,0 +1,31 @@
+#ifndef STIM_UTIL_FILESIZE_H
+#define STIM_UTIL_FILESIZE_H
+
+#ifdef _WIN32
+#include <Windows.h>
+#endif
+
+namespace stim{
+static size_t file_size(std::string filename){
+#ifdef _WIN32
+	HANDLE hFile = CreateFile(filename.c_str(), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+	if(hFile == INVALID_HANDLE_VALUE) return 0;
+	LARGE_INTEGER size;
+	if(!GetFileSizeEx(hFile, &size)){
+		CloseHandle(hFile);
+		return 0;
+	}
+	CloseHandle(hFile);
+	return (size_t)size.QuadPart;
+#elif
+
+
+
+#endif
+}
+
+}	//end namespace stim
+
+
+
+#endif
\ No newline at end of file
--
libgit2 0.21.4