diff --git a/g10/plaintext.c b/g10/plaintext.c
index 5c21dd7f6..d7f9df1f8 100644
--- a/g10/plaintext.c
+++ b/g10/plaintext.c
@@ -476,6 +476,13 @@ handle_plaintext (PKT_plaintext * pt, md_filter_context_t * mfx,
 		state = 1;
 	      else if (c == '\n')
 		state = 2;
+	      else if (c == '\f')
+		{
+		  /* Form feed indicates line truncation - this is a security issue */
+		  log_error ("cleartext signature contains truncated line (form feed detected)\n");
+		  err = gpg_error (GPG_ERR_BAD_SIGNATURE);
+		  goto leave;
+		}
 	      else
 		gcry_md_putc (mfx->md, c);
 	    }
@@ -486,6 +493,12 @@ handle_plaintext (PKT_plaintext * pt, md_filter_context_t * mfx,
 	      else
 		{
 		  gcry_md_putc (mfx->md, '\r');
+		  if (c == '\f')
+		    {
+		      log_error ("cleartext signature contains truncated line (form feed detected)\n");
+		      err = gpg_error (GPG_ERR_BAD_SIGNATURE);
+		      goto leave;
+		    }
 		  if (c == '\r')
 		    state = 1;
 		  else