src/pkg/exp/template/html/css.go      | 11 ++++++++++-
 src/pkg/exp/template/html/css_test.go | 12 ++++++++----

diff --git a/src/pkg/exp/template/html/css.go b/src/pkg/exp/template/html/css.go
index d881328c93cb2e78aa0874b0616f4adcb299ba8c..c22ec6df0d07aa6fdf5b6d5a0a74257a47d8cc2e 100644
--- a/src/pkg/exp/template/html/css.go
+++ b/src/pkg/exp/template/html/css.go
@@ -144,6 +144,15 @@ 	}
 	return c
 }
 
+// isCSSSpace returns whether b is a CSS space char as defined in wc.
+func isCSSSpace(b byte) bool {
+	switch b {
+	case '\t', '\n', '\f', '\r', ' ':
+		return true
+	}
+	return false
+}
+
 // cssEscaper escapes HTML and CSS special characters using \<hex>+ escapes.
 func cssEscaper(args ...interface{}) string {
 	s, _ := stringify(args...)
@@ -198,7 +207,7 @@ 		}
 		b.WriteString(s[written:i])
 		b.WriteString(repl)
 		written = i + utf8.RuneLen(r)
-		if repl != `\\` && (written == len(s) || isHex(s[written])) {
+		if repl != `\\` && (written == len(s) || isHex(s[written]) || isCSSSpace(s[written])) {
 			b.WriteByte(' ')
 		}
 	}
diff --git a/src/pkg/exp/template/html/css_test.go b/src/pkg/exp/template/html/css_test.go
index 5ba3e77bb365710141d928d8c64ec9abfe312d9d..5f633e89442afa955a409ff054b559a1872d730c 100644
--- a/src/pkg/exp/template/html/css_test.go
+++ b/src/pkg/exp/template/html/css_test.go
@@ -100,9 +100,13 @@ 			"The <i>quick</i>,\r\n<span style='color:brown'>brown</span> fox jumps\u2028over the <canine class=\"lazy\">dog</canine>",
 		},
 	}
 	for _, test := range tests {
-		got := string(decodeCSS([]byte(test.css)))
-		if got != test.want {
-			t.Errorf("%q: want\n\t%q\nbut got\n\t%q", test.css, test.want, got)
+		got1 := string(decodeCSS([]byte(test.css)))
+		if got1 != test.want {
+			t.Errorf("%q: want\n\t%q\nbut got\n\t%q", test.css, test.want, got1)
+		}
+		recoded := cssEscaper(got1)
+		if got2 := string(decodeCSS([]byte(recoded))); got2 != test.want {
+			t.Errorf("%q: escape & decode not dual for %q", test.css, recoded)
 		}
 	}
 }
@@ -156,7 +160,7 @@ 		"pqrstuvwxyz{|}~\x7f" +
 		"\u00A0\u0100\u2028\u2029\ufeff\U0001D11E")
 
 	want := ("\\0\x01\x02\x03\x04\x05\x06\x07" +
-		"\x08\\9\\a\x0b\\c\\d\x0E\x0F" +
+		"\x08\\9 \\a\x0b\\c \\d\x0E\x0F" +
 		"\x10\x11\x12\x13\x14\x15\x16\x17" +
 		"\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" +
 		` !\22#$%\26\27\28\29*\2b,-.\2f ` +