diff --git a/lib/linguist/languages.yml b/lib/linguist/languages.yml
index aae547bd83..c4b1a90148 100644
--- a/lib/linguist/languages.yml
+++ b/lib/linguist/languages.yml
@@ -5087,6 +5087,7 @@ PEG.js:
   color: "#234d6b"
   extensions:
   - ".pegjs"
+  - ".peggy"
   tm_scope: source.pegjs
   ace_mode: javascript
   codemirror_mode: javascript
diff --git a/samples/PEG.js/abnfp.peggy b/samples/PEG.js/abnfp.peggy
new file mode 100644
index 0000000000..cb23c2d222
--- /dev/null
+++ b/samples/PEG.js/abnfp.peggy
@@ -0,0 +1,200 @@
+{{
+import * as ast from "./ast.js";
+}}
+
+{
+const rules = new ast.Rules();
+}
+
+rulelist = (rule / empty)+ {
+  rules.loc = location();
+  return rules;
+}
+
+empty
+  = WSP* comment
+  / WSP* CRLF
+
+// Allow starting whitespace before a rule
+rule = WSP* name:rulename operator:defined_as children:elements c_nl {
+  if (operator === "=/") {
+    rules.addAlternate(name, children, location())
+  } else {
+    rules.addRule(name, children, location())
+  }
+}
+
+rulename = $(ALPHA (ALPHA / DIGIT / "-")*)
+
+// RFC 2045 uses :=
+// RFC 1730 uses ::=
+// `::=` is from the original BNF.
+// I don't know where `:=` came from.
+defined_as = c_wsp* @("=/" / ":"|0..2| "=") c_wsp*
+
+elements = @alternation c_wsp*
+
+comment = ";" $(WSP / VCHAR)* EOL
+
+alternation = head:concatenation tail:(c_wsp* "/" c_wsp* @concatenation)* {
+  if (tail.length > 0) {
+    return new ast.Alternation([head, ...tail], location());
+  }
+  return head;
+}
+
+concatenation = head:repetition tail:(c_wsp+ @repetition)* {
+  if (tail.length > 0) {
+    return new ast.Concatenation([head, ...tail], location());
+  }
+  return head;
+}
+
+repetition = repeat:repeat? e:element {
+  if (repeat) {
+    return new ast.Repetition(repeat, e, location());
+  }
+  return e;
+}
+
+repeat
+  = min:decnum? "*" max:decnum? {
+    min |= 0;
+    if (max === 0) {
+      error("max must not be zero");
+      return;
+    }
+    if ((typeof max === "number") && (max < min)) {
+      error(`max must be greater than or equal to min, but ${max} < ${min}`)
+      return;
+    }
+    return new ast.Repeat(min, max, location());
+  }
+  / n:decnum { return new ast.Repeat(n, n, location()); }
+
+element
+  = name:rulename { return rules.addRef(name, location()) }
+  / group
+  / option
+  / char_val
+  / num_val
+  / prose_val
+
+group = "(" c_wsp* alt:alternation c_wsp* ")" {
+  return new ast.Group(alt, location());
+}
+
+option = "[" c_wsp* alt:alternation c_wsp* "]" {
+  const loc = location();
+  return new ast.Repetition(new ast.Repeat(0, 1, loc), alt, loc);
+}
+
+char_val
+  = "%i"i? DQUOTE txt:$([\x20-\x21] / [\x23-\x7e])* DQUOTE {
+    return new ast.CaseInsensitiveString(txt, location());
+  }
+  / "%s"i DQUOTE txt:$([\x20-\x21] / [\x23-\x7e])* DQUOTE {
+    return new ast.CaseSensitiveString(txt, 0, location());
+  }
+
+num_val = "%" @(bin_val / dec_val / hex_val)
+
+prose_val = "<" prose:$([\x20-\x3d] / [\x3f-\x7e] / CRLF)* ">" {
+  return new ast.Prose(prose, location());
+}
+
+DQUOTE = "\""
+
+bin_val
+  = "b"i nums:binnum|2..,"."| {
+    return new ast.CaseSensitiveString(
+      nums.map(b => String.fromCodePoint(b)).join(""),
+      2,
+      location()
+    );
+  }
+  / "b"i min:binnum "-" max:binnum {
+    return ast.Range.create(2, min, max, location());
+  }
+  / "b"i n:binnum {
+    return new ast.CaseSensitiveString(String.fromCodePoint(n), 2, location())
+  }
+
+dec_val
+  = "d"i nums:decnum|2..,"."| {
+    return new ast.CaseSensitiveString(
+      nums.map(d => String.fromCodePoint(d)).join(""),
+      10,
+      location()
+    );
+  }
+  / "d"i min:decnum "-" max:decnum {
+    return ast.Range.create(10, min, max, location());
+  }
+  / "d"i n:decnum {
+    return new ast.CaseSensitiveString(String.fromCodePoint(n), 10, location())
+  }
+
+hex_val
+  = "x"i nums:hexnum|2..,"."| {
+    return new ast.CaseSensitiveString(
+      nums.map(x => String.fromCodePoint(x)).join(""),
+      16,
+      location()
+    );
+  }
+  / "x"i min:hexnum "-" max:hexnum {
+    return ast.Range.create(16, min, max, location());
+  }
+  / "x"i n:hexnum {
+    return new ast.CaseSensitiveString(String.fromCodePoint(n), 10, location())
+  }
+
+binnum = b:$BIT+ { return parseInt(b, 2) }
+decnum = d:$DIGIT+ { return parseInt(d, 10) }
+hexnum = h:$HEXDIG+ { return parseInt(h, 16) }
+
+c_wsp
+  = c_nl WSP
+  / WSP
+
+c_nl
+  = EOL
+  / comment
+
+EOL
+  = CRLF
+  / EOF
+
+EOF
+  = !.
+
+BIT
+  = "0"
+  / "1"
+
+HEXDIG
+  = DIGIT
+  / [A-F]i
+
+ALPHA = [\x41-\x5a] / [\x61-\x7a]
+
+DIGIT = [\x30-\x39]
+
+WSP = SP / HTAB
+
+SP = " "
+
+HTAB = "\t"
+
+VCHAR = [\x21-\x7e]
+
+// Take any CR/LF sequence
+CRLF
+  = CR LF // Windows
+  / LF    // Unix
+  / CR    // Mac
+
+CR = "\r"
+
+LF = "\n"