diff --git a/src/sysdep.c b/src/sysdep.c
index c59034ce5c3..1eaf648ea78 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -3006,7 +3006,11 @@ list_system_processes (void)
   for (tail = proclist; CONSP (tail); tail = next)
     {
       next = XCDR (tail);
-      XSETCAR (tail, Fstring_to_number (XCAR (tail), Qnil));
+      Lisp_Object pidstring = XCAR (tail);
+      Lisp_Object pid = Fstring_to_number (pidstring, Qnil);
+      if (!INTEGERP (pid) || XINT (pid) <= 0)
+	xsignal1 (Qoverflow_error, pidstring);
+      XSETCAR (tail, pid);
     }
 
   /* directory_files_internal returns the files in reverse order; undo
diff --git a/src/xfaces.c b/src/xfaces.c
index 77afee4587d..56df06574a7 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -3393,7 +3393,7 @@ DEFUN ("internal-set-lisp-face-attribute-from-resource",
   else if (EQ (attr, QCheight))
     {
       value = Fstring_to_number (value, make_number (10));
-      if (XINT (value) <= 0)
+      if (!INTEGERP (value) || XINT (value) <= 0)
 	signal_error ("Invalid face height from X resource", value);
     }
   else if (EQ (attr, QCbold) || EQ (attr, QCitalic))