diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 98e82ada635..2d08c82d4e2 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2000-09-17  Joseph S. Myers  <jsm28@cam.ac.uk>
+
+	* c-decl.c (grokdeclarator): Don't give a warning about defaulting
+	to int for plain complex which defaults to complex double.  Do
+	warn about defaulting to complex double if pedantic.  Warn about
+	complex integer types if pedantic.  Warn about complex types if
+	pedantic and not in C99 mode.
+	* c-typeck.c (build_unary_op): If pedantic, warn about use of ~
+	for complex conjugation.
+
 2000-09-17  Joseph S. Myers  <jsm28@cam.ac.uk>
 
 	* contrib.texi: Update my entry.
diff --git a/gcc/c-decl.c b/gcc/c-decl.c
index 1de1f9748c3..8287eefb2e4 100644
--- a/gcc/c-decl.c
+++ b/gcc/c-decl.c
@@ -4078,7 +4078,8 @@ grokdeclarator (declarator, declspecs, decl_context, initialized)
     {
       if ((! (specbits & ((1 << (int) RID_LONG) | (1 << (int) RID_SHORT)
 			  | (1 << (int) RID_SIGNED)
-			  | (1 << (int) RID_UNSIGNED))))
+			  | (1 << (int) RID_UNSIGNED)
+			  | (1 << (int) RID_COMPLEX))))
 	  /* Don't warn about typedef foo = bar.  */
 	  && ! (specbits & (1 << (int) RID_TYPEDEF) && initialized)
 	  && ! in_system_header)
@@ -4209,6 +4210,8 @@ grokdeclarator (declarator, declspecs, decl_context, initialized)
 
   if (specbits & 1 << (int) RID_COMPLEX)
     {
+      if (pedantic && !flag_isoc99)
+	pedwarn ("ISO C89 does not support complex types");
       /* If we just have "complex", it is equivalent to
 	 "complex double", but if any modifiers at all are specified it is
 	 the complex form of TYPE.  E.g, "complex short" is
@@ -4218,9 +4221,17 @@ grokdeclarator (declarator, declspecs, decl_context, initialized)
 	  && ! (specbits & ((1 << (int) RID_LONG) | (1 << (int) RID_SHORT)
 			    | (1 << (int) RID_SIGNED)
 			    | (1 << (int) RID_UNSIGNED))))
-	type = complex_double_type_node;
+	{
+	  if (pedantic)
+	    pedwarn ("ISO C does not support plain `complex' meaning `double complex'");
+	  type = complex_double_type_node;
+	}
       else if (type == integer_type_node)
-	type = complex_integer_type_node;
+	{
+	  if (pedantic)
+	    pedwarn ("ISO C does not support complex integer types");
+	  type = complex_integer_type_node;
+	}
       else if (type == float_type_node)
 	type = complex_float_type_node;
       else if (type == double_type_node)
@@ -4228,7 +4239,11 @@ grokdeclarator (declarator, declspecs, decl_context, initialized)
       else if (type == long_double_type_node)
 	type = complex_long_double_type_node;
       else
-	type = build_complex_type (type);
+	{
+	  if (pedantic)
+	    pedwarn ("ISO C does not support complex integer types");
+	  type = build_complex_type (type);
+	}
     }
 
   /* Figure out the type qualifiers for the declaration.  There are
diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index f4b42b991a5..75fb57a6b61 100644
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -2807,6 +2807,8 @@ build_unary_op (code, xarg, noconvert)
       if (typecode == COMPLEX_TYPE)
 	{
 	  code = CONJ_EXPR;
+	  if (pedantic)
+	    pedwarn ("ISO C does not support `~' for complex conjugation");
 	  if (!noconvert)
 	    arg = default_conversion (arg);
 	}
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3e847d85565..0362ad7f2f6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2000-09-17  Joseph S. Myers  <jsm28@cam.ac.uk>
+
+	* gcc.dg/c90-complex-1.c, gcc.dg/c99-complex-1.c: New tests.
+
 2000-09-17  Greg McGary  <greg@mcgary.org>
 
 	* gcc.c-torture/execute/20000917-1.c: New test.
diff --git a/gcc/testsuite/gcc.dg/c90-complex-1.c b/gcc/testsuite/gcc.dg/c90-complex-1.c
new file mode 100644
index 00000000000..b65fc6873e9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c90-complex-1.c
@@ -0,0 +1,7 @@
+/* Test for _Complex: in C99 only.  */
+/* Origin: Joseph Myers <jsm28@cam.ac.uk> */
+/* { dg-do compile } */
+/* { dg-options "-std=iso9899:1990 -pedantic-errors" } */
+
+_Complex double foo; /* { dg-bogus "warning" "warning in place of error" } */
+/* { dg-error "C" "_Complex not in C90" { target *-*-* } 6 } */
diff --git a/gcc/testsuite/gcc.dg/c99-complex-1.c b/gcc/testsuite/gcc.dg/c99-complex-1.c
new file mode 100644
index 00000000000..2e1ba7df539
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c99-complex-1.c
@@ -0,0 +1,33 @@
+/* Test for _Complex: in C99 only.  A few basic tests.  */
+/* Origin: Joseph Myers <jsm28@cam.ac.uk> */
+/* { dg-do compile } */
+/* { dg-options "-std=iso9899:1999 -pedantic-errors" } */
+
+/* Test _Complex allowed on floating types.  */
+
+float _Complex a;
+_Complex float b;
+double _Complex c;
+_Complex double d;
+long double _Complex e;
+_Complex long double f;
+
+/* Plain `_Complex' for complex double is a GNU extension.  */
+_Complex g; /* { dg-bogus "warning" "warning in place of error" } */
+/* { dg-error "plain" "plain _Complex" { target *-*-* } 16 } */
+
+/* Complex integer types are GNU extensions.  */
+_Complex int h; /* { dg-bogus "warning" "warning in place of error" } */
+/* { dg-error "complex integer" "_Complex int" { target *-*-* } 20 } */
+_Complex long i; /* { dg-bogus "warning" "warning in place of error" } */
+/* { dg-error "complex integer" "_Complex long" { target *-*-* } 22 } */
+
+/* Use of ~ for complex conjugation is a GNU extension, but a constraint
+   violation (6.5.3.3p1) in C99.
+*/
+_Complex double
+foo (_Complex double z)
+{
+  return ~z; /* { dg-bogus "warning" "warning in place of error" } */
+  /* { dg-error "complex conj" "~ for conjugation" { target *-*-* } 31 } */
+}