diff --git a/gcc/fortran/ChangeLog b/gcc/fortran/ChangeLog
index 9c787f73bfd..b3770ce0454 100644
--- a/gcc/fortran/ChangeLog
+++ b/gcc/fortran/ChangeLog
@@ -1,3 +1,9 @@
+2019-09-11  Steven G. Kargl  <kargl@gcc.gnu.org>
+
+	PR fortran/91642
+	* io.c (gfc_match_inquire): null() cannot be in an iolength inquire
+	list.
+
 2019-09-05  Harald Anlauf  <anlauf@gmx.de>
 
 	PR fortran/91496
diff --git a/gcc/fortran/io.c b/gcc/fortran/io.c
index d57b7471da2..bb645602a2c 100644
--- a/gcc/fortran/io.c
+++ b/gcc/fortran/io.c
@@ -4641,6 +4641,17 @@ gfc_match_inquire (void)
       if (m == MATCH_NO)
 	goto syntax;
 
+      for (gfc_code *c = code; c; c = c->next)
+	if (c->expr1 && c->expr1->expr_type == EXPR_FUNCTION
+	    && c->expr1->symtree && c->expr1->symtree->n.sym->attr.function
+	    && !c->expr1->symtree->n.sym->attr.external
+	    && strcmp (c->expr1->symtree->name, "null") == 0)
+	  {
+	    gfc_error ("NULL() near %L cannot appear in INQUIRE statement",
+		       &c->expr1->where);
+	    goto cleanup;
+	  }
+
       new_st.op = EXEC_IOLENGTH;
       new_st.expr1 = inquire->iolength;
       new_st.ext.inquire = inquire;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index aa3127cf3fd..6c316ee7f93 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-09-11  Steven G. Kargl  <kargl@gcc.gnu.org>
+
+	PR fortran/91642
+	* gfortran.dg/pr91642.f90: New test.
+
 2019-09-11  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/89435
diff --git a/gcc/testsuite/gfortran.dg/pr91642.f90 b/gcc/testsuite/gfortran.dg/pr91642.f90
new file mode 100644
index 00000000000..b3cc40f50ec
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr91642.f90
@@ -0,0 +1,19 @@
+! { dg-do compile }
+! PR fortran/91642
+! Code contributed by Gerhard Steinmetz
+program p
+   integer i
+   integer :: iol
+   integer, external :: null
+   i = 0
+   inquire (iolength=iol) null()
+   if (iol == 4) stop 1
+end
+
+subroutine q
+   integer i
+   integer :: iol
+   i = 0
+   inquire (iolength=iol) i, null() ! { dg-error "cannot appear in INQUIRE" }
+   if (iol == 4) stop 2
+end