diff --git a/src/grep.c b/src/grep.c
--- a/src/grep.c
+++ b/src/grep.c
@@ -1415,13 +1415,13 @@ grep (int fd, struct stat const *st)
         }
 
       /* Detect whether leading context is adjacent to previous output.  */
-      if (lastout)
-        {
-          if (textbin == TEXTBIN_UNKNOWN)
-            textbin = TEXTBIN_TEXT;
-          if (beg != lastout)
-            lastout = 0;
-        }
+      if (beg != lastout)
+        lastout = 0;
+
+      /* If the file's textbin has not been determined yet, assume
+         it's text if has found any matched line already.  */
+      if (textbin == TEXTBIN_UNKNOWN && nlines)
+        textbin = TEXTBIN_TEXT;
 
       /* Handle some details and read more data to scan.  */
       save = residue + lim - beg;