diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 65b6b2f9bd0..8a295d6c324 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2006-07-18  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>
+
+	PR c/28286
+	* c-pragma.c (handle_pragma_pack): Handle invalid constants.
+
 2006-07-18  Alexandre Oliva  <aoliva@redhat.com>
 
 	PR c/26993
diff --git a/gcc/c-pragma.c b/gcc/c-pragma.c
index e71ab07a16f..b2712acc937 100644
--- a/gcc/c-pragma.c
+++ b/gcc/c-pragma.c
@@ -160,6 +160,8 @@ handle_pragma_pack (cpp_reader * ARG_UNUSED (dummy))
     }
   else if (token == CPP_NUMBER)
     {
+      if (TREE_CODE (x) != INTEGER_CST)
+	GCC_BAD ("invalid constant in %<#pragma pack%> - ignored");
       align = TREE_INT_CST_LOW (x);
       action = set;
       if (pragma_lex (&x) != CPP_CLOSE_PAREN)
@@ -190,6 +192,8 @@ handle_pragma_pack (cpp_reader * ARG_UNUSED (dummy))
 	    }
 	  else if (token == CPP_NUMBER && action == push && align == -1)
 	    {
+	      if (TREE_CODE (x) != INTEGER_CST)
+		GCC_BAD ("invalid constant in %<#pragma pack%> - ignored");
 	      align = TREE_INT_CST_LOW (x);
 	      if (align == -1)
 		action = set;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9638bcf78d4..0828f4aaa2a 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2006-07-18  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>
+
+	PR c/28286
+	* gcc.dg/pragma-pack-4.c: New test.
+
 2006-07-17  Steve Ellcey  <sje@cup.hp.com>
 
 	PR c++/28291
diff --git a/gcc/testsuite/gcc.dg/pragma-pack-4.c b/gcc/testsuite/gcc.dg/pragma-pack-4.c
new file mode 100644
index 00000000000..1765591f43c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pragma-pack-4.c
@@ -0,0 +1,6 @@
+/* PR c/28286 */
+/* { dg-do compile } */
+
+#pragma pack(0.5)         /* { dg-warning "invalid constant" } */
+#pragma pack(push,0.5)    /* { dg-warning "invalid constant" } */
+#pragma pack(push,x,0.5)  /* { dg-warning "invalid constant" } */