diff --git a/ChangeLog b/ChangeLog
index e418956208..d02a755408 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Thu Jul 24 16:41:31 2003  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
+
+	* lib/mkmf.rb (have_type): check if a type is defined.
+
+	* lib/mkmf.rb (check_sizeof): check size of a type.
+
+	* ext/dbm/extconf.rb: check if type DBM is defined.
+	  [ruby-talk:76693]
+
 Thu Jul 24 16:18:40 2003  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
 
 	* ChangeLog (add-log-time-format): "%c" contains timezone on
diff --git a/ext/dbm/extconf.rb b/ext/dbm/extconf.rb
index 1fc443c280..5a67603e69 100644
--- a/ext/dbm/extconf.rb
+++ b/ext/dbm/extconf.rb
@@ -32,7 +32,7 @@ def db_check(db)
 
   if have_library(db, db_prefix("dbm_open")) || have_func(db_prefix("dbm_open"))
     for hdr in $dbm_conf_headers.fetch(db, ["ndbm.h"])
-      if have_header(hdr.dup)
+      if have_header(hdr.dup) and have_type("DBM", hdr.dup, hsearch)
 	$CFLAGS += " " + hsearch + '-DDBM_HDR="<'+hdr+'>"'
 	return true
       end
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 513e7683b5..51eb169217 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -249,6 +249,60 @@ def cpp_include(header)
   end
 end
 
+def try_static_assert(expr, headers = nil, opt = "")
+  headers = cpp_include(headers)
+  try_compile(<<SRC, opt)
+#{COMMON_HEADERS}
+#{headers}
+int tmp[(#{expr}) ? 1 : -1];
+SRC
+end
+
+def try_constant(const, headers = nil, opt = "")
+  if true # CROSS_COMPILING
+    unless try_compile(<<"SRC", opt)
+#{COMMON_HEADERS}
+#{cpp_include(headers)}
+int tmp = #{const};
+SRC
+      return nil
+    end
+    if try_static_assert("#{const} < 0", headers, opt)
+      neg = true
+      const = "-(#{const})"
+    elsif try_static_assert("#{const} == 0", headers, opt)
+      return 0
+    end
+    upper = 1
+    until try_static_assert("#{const} < #{upper}", headers, opt)
+      lower = upper
+      upper <<= 1
+    end
+    return nil unless lower
+    until try_static_assert("#{const} == #{upper}", headers, opt)
+      if try_static_assert("#{const} > #{(upper+lower)/2}", headers, opt)
+        lower = (upper+lower)/2
+      else
+        upper = (upper+lower)/2
+      end
+    end
+    upper = -upper if neg
+    return upper
+  else
+    src = %{#{COMMON_HEADERS}
+#{cpp_include(headers)}
+#include <stdio.h>
+int main() {printf("%d\\n", (int)(#{const})); return 0;}
+}
+    if try_link0(src, opt)
+      xpopen("./conftest") do |f|
+        return Integer(f.gets)
+      end
+    end
+  end
+  nil
+end
+
 def try_func(func, libs, headers = nil)
   headers = cpp_include(headers)
   try_link(<<"SRC", libs) or try_link(<<"SRC", libs)
@@ -442,6 +496,38 @@ SRC
   end
 end
 
+def have_type(type, header=nil, opt="")
+  checking_for type do
+    if try_compile(<<"SRC", opt) or try_compile(<<"SRC", opt)
+#{COMMON_HEADERS}
+#{cpp_include(header)}
+static #{type} t;
+SRC
+#{COMMON_HEADERS}
+#{cpp_include(header)}
+static #{type} *t;
+SRC
+      $defs.push(format("-DHAVE_TYPE_%s", type.upcase))
+      true
+    else
+      false
+    end
+  end
+end
+
+def check_sizeof(type, header=nil)
+  expr = "sizeof(#{type})"
+  m = "checking size of #{type}... "
+  message "%s", m
+  Logging::message "check_sizeof: %s--------------------\n", m
+  if size = try_constant(expr, header)
+    $defs.push(format("-DSIZEOF_%s", type.upcase))
+  end
+  message(a = size ? "#{size}\n" : "failed\n")
+  Logging::message "-------------------- %s\n", a
+  r
+end
+
 def find_executable0(bin, path = nil)
   path = (path || ENV['PATH']).split(File::PATH_SEPARATOR)
   ext = config_string('EXEEXT')