diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bf5617d263d5380f5f383df91a26b63aa3fbd3ad..8526cfb6c88314fdb66692cab320abe7fa9203ce 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2004-03-11  Ulrich Weigand  <uweigand@de.ibm.com>
+
+	* combine.c (if_then_else_cond): Check for NULL return value of
+	simplify_gen_subreg.
+
 2004-03-11  Richard Sandiford  <rsandifo@redhat.com>
 
 	PR target/14496
diff --git a/gcc/combine.c b/gcc/combine.c
index 497e8263ad97efe568d2ec935821162b854576e3..c627187c17415f232350a41bac7be43e5a3f263c 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7378,12 +7378,16 @@ if_then_else_cond (rtx x, rtx *ptrue, rtx *pfalse)
 	   && 0 != (cond0 = if_then_else_cond (SUBREG_REG (x),
 					       &true0, &false0)))
     {
-      *ptrue = simplify_gen_subreg (mode, true0,
+      true0 = simplify_gen_subreg (mode, true0,
+				   GET_MODE (SUBREG_REG (x)), SUBREG_BYTE (x));
+      false0 = simplify_gen_subreg (mode, false0,
 				    GET_MODE (SUBREG_REG (x)), SUBREG_BYTE (x));
-      *pfalse = simplify_gen_subreg (mode, false0,
-				     GET_MODE (SUBREG_REG (x)), SUBREG_BYTE (x));
-
-      return cond0;
+      if (true0 && false0)
+	{
+	  *ptrue = true0;
+	  *pfalse = false0;
+	  return cond0;
+	}
     }
 
   /* If X is a constant, this isn't special and will cause confusions
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 90916b8b98a76f5b205c3581ff0e206b2589bf0f..da07a0408e901a5f6544c1ce9237edcc076e4294 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2004-03-11  Ulrich Weigand  <uweigand@de.ibm.com>
+
+	* gcc.dg/20040310-1.c: New test.
+
 2004-03-11  Roger Sayle  <roger@eyesopen.com>
 
 	* gcc.c-torture/execute/20040311-1.c: New test case.
diff --git a/gcc/testsuite/gcc.dg/20040310-1.c b/gcc/testsuite/gcc.dg/20040310-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..104e98d08893e895fe890d3f4f5ffcd0a00a5457
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20040310-1.c
@@ -0,0 +1,34 @@
+/* This caused cc1 to segfault on s390x-ibm-linux
+   due to a bug in if_then_else_cond (combine.c).  */
+
+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+
+extern void use (unsigned int x);
+
+int main (void)
+{
+  union 
+    {
+      unsigned int x;
+      unsigned long pad;
+    } A;
+
+  struct 
+    {
+      unsigned int x : 1;
+    } B;
+
+  A.x = 1;
+  B.x = 1;
+  A.x /= B.x;
+  use (A.x);
+
+  A.x = 1;
+  B.x = 1;
+  B.x /= A.x;
+  use (B.x);
+
+  return 0;
+}
+