diff --git a/logging.c b/logging.c
index c3634274..41c5b257 100644
--- a/logging.c
+++ b/logging.c
@@ -164,7 +164,6 @@ void logfopen(void *handle)
 {
     struct LogContext *ctx = (struct LogContext *)handle;
     struct tm tm;
-    FILE *fp;
     int mode;
 
     /* Prevent repeat calls */
@@ -184,10 +183,8 @@ void logfopen(void *handle)
                    conf_get_str(ctx->conf, CONF_host),
                    conf_get_int(ctx->conf, CONF_port), &tm);
 
-    fp = f_open(ctx->currlogfilename, "r", FALSE);  /* file already present? */
-    if (fp) {
+    if (open_for_write_would_lose_data(ctx->currlogfilename)) {
 	int logxfovr = conf_get_int(ctx->conf, CONF_logxfovr);
-	fclose(fp);
 	if (logxfovr != LGXF_ASK) {
 	    mode = ((logxfovr == LGXF_OVR) ? 2 : 1);
 	} else
diff --git a/putty.h b/putty.h
index 4c64cb85..76ab6fb7 100644
--- a/putty.h
+++ b/putty.h
@@ -1467,6 +1467,7 @@ Filename *filename_deserialise(void *data, int maxsize, int *used);
 char *get_username(void);	       /* return value needs freeing */
 char *get_random_data(int bytes, const char *device); /* used in cmdgen.c */
 char filename_char_sanitise(char c);   /* rewrite special pathname chars */
+int open_for_write_would_lose_data(const Filename *fn);
 
 /*
  * Exports and imports from timing.c.
diff --git a/unix/uxmisc.c b/unix/uxmisc.c
index daa61a01..50d385b6 100644
--- a/unix/uxmisc.c
+++ b/unix/uxmisc.c
@@ -349,3 +349,14 @@ char *make_dir_path(const char *path, mode_t mode)
         pos += strspn(path + pos, "/");
     }
 }
+
+int open_for_write_would_lose_data(const Filename *fn)
+{
+    FILE *fp;
+    if ((fp = f_open(fn, "r", FALSE)) != NULL) {
+        fclose(fp);
+        return TRUE;
+    } else {
+        return FALSE;
+    }
+}
diff --git a/windows/winmisc.c b/windows/winmisc.c
index fca8af01..75a95c6a 100644
--- a/windows/winmisc.c
+++ b/windows/winmisc.c
@@ -587,3 +587,14 @@ FontSpec *fontspec_deserialise(void *vdata, int maxsize, int *used)
                         GET_32BIT_MSB_FIRST(end + 4),
                         GET_32BIT_MSB_FIRST(end + 8));
 }
+
+int open_for_write_would_lose_data(const Filename *fn)
+{
+    FILE *fp;
+    if ((fp = f_open(fn, "r", FALSE)) != NULL) {
+        fclose(fp);
+        return TRUE;
+    } else {
+        return FALSE;
+    }
+}