diff --git a/README.md b/README.md
index c2105ce..46b0b26 100644
--- a/README.md
+++ b/README.md
@@ -240,7 +240,7 @@ as follows:
 
 - _**<ternary>** ::= "(" expression ")" "?" expression ":" expression._
 
-- _**<envref>** ::= letter | "_" { letter | digit | "_" }.\_
+- _**<envref>** ::= letter | "_" { letter | digit | "_"  | "." }.\_
 
 - _**<var>** ::= envref._
 
diff --git a/project.clj b/project.clj
index ce3a3a0..8a2d500 100644
--- a/project.clj
+++ b/project.clj
@@ -1,4 +1,4 @@
-(defproject rm-hull/infix "0.4.2"
+(defproject rm-hull/infix "0.4.3"
   :description "A small Clojure library for expressing LISP expressions as infix rather than prefix notation"
   :url "https://github.com/rm-hull/infix"
   :license {
diff --git a/src/infix/grammar.clj b/src/infix/grammar.clj
index 6adc354..a87c971 100644
--- a/src/infix/grammar.clj
+++ b/src/infix/grammar.clj
@@ -38,7 +38,7 @@
 ;
 ; function ::= envref expression | envref "(" <empty> | expression { "," expression } ")".
 ; ternary ::= expression "?" expression ":" expression.
-; envref ::= letter | "_" { letter | digit | "_" }.
+; envref ::= letter | "_" { letter | digit | "_"  | "." }.
 ; var ::= envref.
 ; boolean :: = "true" | "false"
 ; number ::= integer | decimal | rational | binary | hex
@@ -56,7 +56,7 @@
 ; TODO: allow unicode/utf8 characters
 (def letter (from-re #"[a-zA-Z]"))
 
-(def alpha-num (any-of letter digit (match "_")))
+(def alpha-num (any-of letter digit (match "_") (match ".")))
 
 (def digits
   (m/do*
@@ -65,7 +65,7 @@
 
 (def envref
   (m/do*
-   (fst <- (any-of letter (match "_")))
+   (fst <- (any-of letter (match "_") (match ".")))
    (rst <- (token (many alpha-num)))
    (m/return (let [kw (keyword (strip-location (cons fst rst)))]
                (fn [env]
diff --git a/test/infix/grammar_test.clj b/test/infix/grammar_test.clj
index edc3f62..8aa4484 100644
--- a/test/infix/grammar_test.clj
+++ b/test/infix/grammar_test.clj
@@ -37,10 +37,11 @@
      (<= (Math/abs (- x y)) (* scale epsilon)))))
 
 (deftest check-var
-  (let [env {:x 32 :something_else 19}]
+  (let [env {:x 32 :something_else 19 :dot.var 608}]
     (is (thrown? ParseException (parse-all var "54")))
     (is (= 32 ((parse-all var "x") env)))
     (is (= 19 ((parse-all var "something_else") env)))
+    (is (= 608 ((parse-all var "dot.var") env)))
     (is (thrown? IllegalStateException ((parse-all var "fred") env)))))
 
 (deftest check-integer
@@ -110,12 +111,13 @@
     (is (thrown? clojure.lang.ArityException ((parse-all function "sqrt(7, 5)") env)))))
 
 (deftest check-expression
-  (let [env (merge base-env {:t 0.324 :x_y_z 3 :_a 4})]
+  (let [env (merge base-env {:t 0.324 :x_y_z 3 :_a 4 :_a.b 2})]
     (is (float= 1.4176457261295824 ((parse-all expression "sin(2 * t) + 3 * cos(4 * t)") env)))
     (is (thrown? IllegalStateException ((parse-all expression "3 + 4") {})))
     (is (= 43 ((parse-all expression "3 + 5 * 8") env)))
     (is (= 64 ((parse-all expression "(3 + 5) * 8") env)))
-    (is (= 10 ((parse-all expression "x_y_z * 2 + _a") env)))))
+    (is (= 10 ((parse-all expression "x_y_z * 2 + _a") env)))
+    (is (= 8 ((parse-all expression "x_y_z * 2 + _a / _a.b") env)))))
 
 (deftest check-ternary-op
   (let [env (merge base-env {:t 150 :x 10 :y 20})]