diff --git a/auto/bin/make.pl b/auto/bin/make.pl
index 6aa1e83..d418bfe 100755
--- a/auto/bin/make.pl
+++ b/auto/bin/make.pl
@@ -9,7 +9,7 @@
 my %regex = (
     extname  => qr/^[A-Z][A-Za-z0-9_]+$/,
     exturl   => qr/^http.+$/,
-    function => qr/^(.+) ([a-z][a-z0-9_]*) \((.+)\)$/i, 
+    function => qr/^(.+) ([a-z][a-z0-9_]*) \((.+)\)\s*(~.*)?$/i, 
     token    => qr/^([A-Z][A-Z0-9_x]*)\s+((?:0x)?[0-9A-Fa-f]+|[A-Z][A-Z0-9_]*)$/,
     type     => qr/^typedef\s+(.+)$/,
     exact    => qr/.*;$/,
@@ -122,10 +122,11 @@ sub parse_ext($)
             }
             elsif (/$regex{function}/)
             {
-                my ($return, $name, $parms) = ($1, $2, $3);
+                my ($return, $name, $parms, $deleted) = ($1, $2, $3, $4);
                 $functions{$name} = {
 		    rtype => $return,
 		    parms => $parms,
+		    deleted => $deleted,
 		};
             } else {
                 print STDERR "'$_' matched no regex.\n";
diff --git a/auto/bin/make_def_fun.pl b/auto/bin/make_def_fun.pl
index 2ed8b4e..f2df301 100755
--- a/auto/bin/make_def_fun.pl
+++ b/auto/bin/make_def_fun.pl
@@ -12,9 +12,18 @@ use warnings;
 
 do 'bin/make.pl';
 
+our %defined = ();
+
 # function pointer declaration
 sub make_pfn_decl($%)
 {
+    our %defined;
+
+    if( $defined{$_[0]} )  # avoid duplicate definitions
+    {
+	return "";
+    }
+    $defined{$_[0]} = 1;
     return "PFN" . (uc $_[0]) . "PROC " . prefixname($_[0]) . " = NULL;";
 }
 
diff --git a/auto/bin/make_header.pl b/auto/bin/make_header.pl
index 5c7f94a..a5d71d1 100755
--- a/auto/bin/make_header.pl
+++ b/auto/bin/make_header.pl
@@ -24,20 +24,89 @@ sub make_type($$)
     return "@_;"
 }
 
+sub make_condition($)
+{
+    my $condition = "";
+    my $needop = 0;
+
+    for my $tok (split(/\s+/, $_[0])) {
+	if ($tok eq "~") {
+	    # ignore
+	} elsif ($tok eq '&&') {
+	    $condition .= ' && ';
+	    $needop = 0;
+	} elsif ($tok eq '||') {
+	    $condition .= ") || (";
+	    $needop = 0;
+	} else {
+	    if ($needop) {
+		$condition .= ' && ';
+	    }
+	    if ($tok =~ /^\d/) {
+		# GL Version
+		$tok =~ s/[.]/_/g;
+		$condition .= "GL_VERSION_${tok}";
+	    } elsif ($tok eq "core") {
+		$condition .= " 0 ";
+	    } elsif ($tok eq "forward") {
+		$condition .= " 0 ";
+	    }
+	    $needop = 1;
+	}
+    }
+
+    # optimize expression
+    $condition = "(" . $condition . ")";
+    $condition =~ s/[(][^)]* 0 [^)]*[)]/ 0 /g;
+    $condition =~ s/\|\|\s*0\s*//g;
+    $condition =~ s/\s*0\s*\|\|//g;
+    $condition =~ s/\s+0\s+/ 0 /g;
+
+    if ($condition eq " 0 ") {
+	return "1";
+    } else {
+	return "!($condition)";
+    }
+}
+
 # function pointer type declaration
 sub make_pfn_type($%)
 {
     our $api;
-    return join(' ', "typedef", $_[1]->{rtype},
+    my $prefix = "";
+    my $suffix = "";
+
+    if ($_[1]->{deleted})
+    {
+	$prefix = "#if " . make_condition($_[1]->{deleted}) . "\n";
+	if ($prefix eq "#if 1\n") {
+	    $prefix = ""; # if optimized away
+	} else {
+	    $suffix = "\n#endif";
+	}
+    }
+    return $prefix . join(' ', "typedef", $_[1]->{rtype},
         "($api * PFN" . (uc $_[0]) . "PROC)",
-        "(" . $_[1]->{parms} . ")") . ";";
+        "(" . $_[1]->{parms} . ")") . ";" . $suffix;
 }
 
 # function name alias
 sub make_pfn_alias($%)
 {
     our $type;
-    return join(" ", "#define", $_[0], $type . "EW_GET_FUN(" . prefixname($_[0]) . ")")
+    my $prefix = "";
+    my $suffix = "";
+
+    if ($_[1]->{deleted})
+    {
+	$prefix = "#if " . make_condition($_[1]->{deleted}) . "\n";
+	if ($prefix eq "#if 1\n") {
+	    $prefix = ""; # if optimized away
+	} else {
+	    $suffix = "\n#endif";
+	}
+    }
+    return $prefix . join(" ", "#define", $_[0], $type . "EW_GET_FUN(" . prefixname($_[0]) . ")") . $suffix;
 }
 
 my @extlist = ();
diff --git a/auto/bin/make_init.pl b/auto/bin/make_init.pl
index 343a1ad..6bc18ec 100755
--- a/auto/bin/make_init.pl
+++ b/auto/bin/make_init.pl
@@ -18,7 +18,38 @@ do 'bin/make.pl';
 sub make_pfn_def_init($%)
 {
     #my $name = prefixname($_[0]);
-    return "  r = ((" . $_[0] . " = (PFN" . (uc $_[0]) . "PROC)glewGetProcAddress((const GLubyte*)\"" . $_[0] . "\")) == NULL) || r;";
+    my $condition = "";
+    if ($_[1]{deleted}) {
+	my $needop = 0;
+
+	for my $tok (split(/\s+/, $_[1]{deleted})) {
+	    if ($tok eq "~") {
+		# ignore
+	    } elsif ($tok eq '&&') {
+		$condition .= ' && ';
+		$needop = 0;
+	    } elsif ($tok eq '||') {
+		$condition .= ') || (';
+		$needop = 0;
+	    } else {
+		if ($needop) {
+		    $condition .= ' && ';
+		}
+		if ($tok =~ /^\d/) {
+		    # GL Version
+		    $tok =~ s/[.]/_/g;
+		    $condition .= "GLEW_VERSION_${tok}";
+		} elsif ($tok eq "core") {
+		    $condition .= "(context_profile & GL_CONTEXT_CORE_PROFILE_BIT)";
+		} elsif ($tok eq "forward") {
+		    $condition .= "(context_flags & GL_CONTEXT_FLAG_FORWARD_COMPATIBLE_BIT)";
+		}
+		$needop = 1;
+	    }
+	}
+	$condition = "if( !(($condition)) ) ";
+    }
+    return "  ${condition}r = ((" . $_[0] . " = (PFN" . (uc $_[0]) . "PROC)glewGetProcAddress((const GLubyte*)\"" . $_[0] . "\")) == NULL) || r;";
 }
 
 sub make_reuse_call($%)
diff --git a/auto/bin/make_struct_fun.pl b/auto/bin/make_struct_fun.pl
index 3eedafe..5eb1822 100755
--- a/auto/bin/make_struct_fun.pl
+++ b/auto/bin/make_struct_fun.pl
@@ -12,10 +12,19 @@ use warnings;
 
 do 'bin/make.pl';
 
+our %defined = ();
+
 # function pointer declaration
 sub make_pfn_decl($%)
 {
     our $export;
+    our %defined;
+
+    if( $defined{$_[0]} )  # avoid duplicate definitions
+    {
+	return "";
+    }
+    $defined{$_[0]} = 1;
     return $export . " PFN" . (uc $_[0]) . "PROC " . prefixname($_[0]) . ";";
 }