diff --git a/src/libCom/osi/os/default/epicsReadline.c b/src/libCom/osi/os/default/epicsReadline.c
index e1bba4c92..f933884ed 100644
--- a/src/libCom/osi/os/default/epicsReadline.c
+++ b/src/libCom/osi/os/default/epicsReadline.c
@@ -28,7 +28,7 @@
 char * epicsShareAPI
 epicsReadline (FILE *fp, const char *prompt)
 {
-    char c;
+    int c;	/* char is unsigned on some archs, EOF is -ve */
     char *line = NULL;
     int linelen = 0;
     int linesize = 50;