diff --git a/README.md b/README.md
index d4a0425..e6f464d 100644
--- a/README.md
+++ b/README.md
@@ -16,10 +16,11 @@ Install
 Configure
 ---------
 * You will need to set the following environment variables in your login file to run **strf**.
-	* `ST_DATADIR` path to **strf** directory (e.g. `$HOME/software/strf`)
+	* `ST_DATADIR` path to **strf** directory (e.g. `$HOME/software/strf`, default: './')
 	* `ST_TLEDIR` path to TLE directory (e.g. `$HOME/tle`)
 	* `ST_COSPAR` COSPAR site number (add to site location to `$ST_DATADIR/data/sites.txt`)
 	* `ST_LOGIN` space-track.org login info (of the form `ST_LOGIN="identity=username&password=password"`)
+    * `ST_SITES_TXT` path to sites.txt (optional, default: `$ST_DATADIR/data/sites.txt`)
 * Run `tleupdate` to download latest TLEs.
 * You should install NTP support on the system and configure time/date to automatically
   synchronize to time servers.
diff --git a/rfsites.c b/rfsites.c
index 58b60b0..b00bd27 100644
--- a/rfsites.c
+++ b/rfsites.c
@@ -16,12 +16,19 @@ site_t get_site(int site_id) {
   float alt;
   char abbrev[3],observer[64];
   site_t s;
-  char *env,filename[LIM];
+  char *env_datadir,*env_sites_txt,filename[LIM];
 
-  env=getenv("ST_DATADIR");
-  if(env==NULL||strlen(env)==0)
-    env=".";
-  sprintf(filename,"%s/data/sites.txt",env);
+  env_datadir = getenv("ST_DATADIR");
+  if (env_datadir == NULL || strlen(env_datadir) == 0) {
+    env_datadir = ".";
+  }
+
+  env_sites_txt = getenv("ST_SITES_TXT");
+  if (env_sites_txt == NULL || strlen(env_sites_txt) == 0) {
+    sprintf(filename, "%s/data/sites.txt", env_datadir);
+  } else {
+    sprintf(filename, "%s", env_datadir);
+  }
 
   file=fopen(filename,"r");
   if (file==NULL) {