diff --git a/src/character_set.rs b/src/character_set.rs
new file mode 100644
index 00000000..143af902
--- /dev/null
+++ b/src/character_set.rs
@@ -0,0 +1,18 @@
+macro_rules! character_set {
+    () => {{
+        [false; 256]
+    }};
+
+    ($value:literal $(,$rest:literal)*) => {{
+        const A: &[u8] = $value;
+        let mut a = character_set!($($rest),*);
+        let mut i = 0;
+        while i < A.len() {
+            a[A[i] as usize] = true;
+            i += 1;
+        }
+        a
+    }}
+}
+
+pub(crate) use character_set;
diff --git a/src/html.rs b/src/html.rs
index 72fd1f0d..eb542c5d 100644
--- a/src/html.rs
+++ b/src/html.rs
@@ -1,4 +1,5 @@
 //! The HTML renderer for the CommonMark AST, as well as helper functions.
+use crate::character_set::character_set;
 use crate::ctype::isspace;
 use crate::nodes::{
     AstNode, ListType, NodeCode, NodeFootnoteDefinition, NodeMath, NodeTable, NodeValue,
@@ -135,42 +136,6 @@ struct HtmlFormatter<'o> {
     plugins: &'o Plugins<'o>,
 }
 
-#[rustfmt::skip]
-const NEEDS_ESCAPED : [bool; 256] = [
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, true,  false, false, false, true,  false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, true, false, true, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-    false, false, false, false, false, false, false, false,
-];
-
 fn tagfilter(literal: &[u8]) -> bool {
     static TAGFILTER_BLACKLIST: [&str; 9] = [
         "title",
@@ -254,9 +219,11 @@ fn dangerous_url(input: &[u8]) -> bool {
 /// Note that this is appropriate and sufficient for free text, but not for
 /// URLs in attributes.  See escape_href.
 pub fn escape(output: &mut dyn Write, buffer: &[u8]) -> io::Result<()> {
+    const HTML_UNSAFE: [bool; 256] = character_set!(b"&<>\"");
+
     let mut offset = 0;
     for (i, &byte) in buffer.iter().enumerate() {
-        if NEEDS_ESCAPED[byte as usize] {
+        if HTML_UNSAFE[byte as usize] {
             let esc: &[u8] = match byte {
                 b'"' => b"&quot;",
                 b'&' => b"&amp;",
@@ -297,16 +264,11 @@ pub fn escape(output: &mut dyn Write, buffer: &[u8]) -> io::Result<()> {
 /// the string "a b", rather than "?q=a%2520b", a search for the literal
 /// string "a%20b".
 pub fn escape_href(output: &mut dyn Write, buffer: &[u8]) -> io::Result<()> {
-    static HREF_SAFE: Lazy<[bool; 256]> = Lazy::new(|| {
-        let mut a = [false; 256];
-        for &c in b"-_.+!*(),%#@?=;:/,+$~abcdefghijklmnopqrstuvwxyz".iter() {
-            a[c as usize] = true;
-        }
-        for &c in b"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".iter() {
-            a[c as usize] = true;
-        }
-        a
-    });
+    const HREF_SAFE: [bool; 256] = character_set!(
+        b"-_.+!*(),%#@?=;:/,+$~",
+        b"abcdefghijklmnopqrstuvwxyz",
+        b"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+    );
 
     let size = buffer.len();
     let mut i = 0;
diff --git a/src/lib.rs b/src/lib.rs
index 3abdb656..3a2ba0ef 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -67,6 +67,7 @@ use std::io::BufWriter;
 
 pub mod adapters;
 pub mod arena_tree;
+mod character_set;
 mod cm;
 mod ctype;
 mod entity;
diff --git a/src/parser/autolink.rs b/src/parser/autolink.rs
index ca377f35..456f9293 100644
--- a/src/parser/autolink.rs
+++ b/src/parser/autolink.rs
@@ -1,7 +1,7 @@
+use crate::character_set::character_set;
 use crate::ctype::{isalnum, isalpha, isspace};
 use crate::nodes::{AstNode, NodeLink, NodeValue};
 use crate::parser::inlines::make_inline;
-use once_cell::sync::Lazy;
 use std::str;
 use typed_arena::Arena;
 use unicode_categories::UnicodeCategories;
@@ -74,13 +74,7 @@ pub fn www_match<'a>(
     i: usize,
     relaxed_autolinks: bool,
 ) -> Option<(&'a AstNode<'a>, usize, usize)> {
-    static WWW_DELIMS: Lazy<[bool; 256]> = Lazy::new(|| {
-        let mut sc = [false; 256];
-        for c in &[b'*', b'_', b'~', b'(', b'['] {
-            sc[*c as usize] = true;
-        }
-        sc
-    });
+    const WWW_DELIMS: [bool; 256] = character_set!(b"*_~([");
 
     if i > 0 && !isspace(contents[i - 1]) && !WWW_DELIMS[contents[i - 1] as usize] {
         return None;
@@ -167,13 +161,7 @@ fn is_valid_hostchar(ch: char) -> bool {
 }
 
 fn autolink_delim(data: &[u8], mut link_end: usize, relaxed_autolinks: bool) -> usize {
-    static LINK_END_ASSORTMENT: Lazy<[bool; 256]> = Lazy::new(|| {
-        let mut sc = [false; 256];
-        for c in &[b'?', b'!', b'.', b',', b':', b'*', b'_', b'~', b'\'', b'"'] {
-            sc[*c as usize] = true;
-        }
-        sc
-    });
+    const LINK_END_ASSORTMENT: [bool; 256] = character_set!(b"?!.,:*_~'\"");
 
     for (i, &b) in data.iter().enumerate().take(link_end) {
         if b == b'<' {
@@ -311,13 +299,7 @@ fn email_match<'a>(
     i: usize,
     relaxed_autolinks: bool,
 ) -> Option<(&'a AstNode<'a>, usize, usize)> {
-    static EMAIL_OK_SET: Lazy<[bool; 256]> = Lazy::new(|| {
-        let mut sc = [false; 256];
-        for c in &[b'.', b'+', b'-', b'_'] {
-            sc[*c as usize] = true;
-        }
-        sc
-    });
+    const EMAIL_OK_SET: [bool; 256] = character_set!(b".+-_");
 
     let size = contents.len();
 
diff --git a/src/xml.rs b/src/xml.rs
index 0dceabf3..3032efbd 100644
--- a/src/xml.rs
+++ b/src/xml.rs
@@ -1,6 +1,6 @@
+use crate::character_set::character_set;
 use crate::nodes::{AstNode, ListType, NodeCode, NodeMath, NodeTable, NodeValue};
 use crate::parser::{Options, Plugins};
-use once_cell::sync::Lazy;
 use std::cmp;
 use std::io::{self, Write};
 
@@ -48,17 +48,11 @@ impl<'o> XmlFormatter<'o> {
     }
 
     fn escape(&mut self, buffer: &[u8]) -> io::Result<()> {
-        static XML_SAFE: Lazy<[bool; 256]> = Lazy::new(|| {
-            let mut a = [true; 256];
-            for &c in b"&<>\"".iter() {
-                a[c as usize] = false;
-            }
-            a
-        });
+        const XML_UNSAFE: [bool; 256] = character_set!(b"&<>\"");
 
         let mut offset = 0;
         for (i, &byte) in buffer.iter().enumerate() {
-            if !XML_SAFE[byte as usize] {
+            if XML_UNSAFE[byte as usize] {
                 let esc: &[u8] = match byte {
                     b'"' => b"&quot;",
                     b'&' => b"&amp;",