diff --git a/gpssim.c b/gpssim.c
index c37435e..b32bb16 100644
--- a/gpssim.c
+++ b/gpssim.c
@@ -1956,6 +1956,11 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "ERROR: No ephemeris available.\n");
 		exit(1);
 	}
+	else if (neph==-1)
+	{
+		fprintf(stderr, "ERROR: ephemeris file not found.\n");
+		exit(1);
+	}
 
 	if ((verb==TRUE)&&(ionoutc.vflg==TRUE))
 	{