diff --git a/lib/lexer.js b/lib/lexer.js
index 9cc03109..33b84ca1 100644
--- a/lib/lexer.js
+++ b/lib/lexer.js
@@ -139,8 +139,13 @@
         tag = 'LEADING_WHEN';
       }
       this.i += id.length;
-      if (!accessed && include(COFFEE_ALIASES, id)) {
-        tag = (id = CONVERSIONS[id]);
+      if (!accessed) {
+        if (include(COFFEE_ALIASES, id)) {
+          tag = (id = CONVERSIONS[id]);
+        }
+        if (this.prev() && this.prev()[0] === 'ASSIGN' && include(HALF_ASSIGNMENTS, tag)) {
+          return this.tag_half_assignment(tag);
+        }
       }
       this.token(tag, id);
       return true;
@@ -339,7 +344,7 @@
     // here. `;` and newlines are both treated as a `TERMINATOR`, we distinguish
     // parentheses that indicate a method call from regular parentheses, and so on.
     Lexer.prototype.literal_token = function literal_token() {
-      var last, match, prev_spaced, space, tag, value;
+      var match, prev_spaced, space, tag, value;
       match = this.chunk.match(OPERATOR);
       value = match && match[1];
       space = match && match[2];
@@ -373,11 +378,9 @@
       }
       this.i += value.length;
       if (space && prev_spaced && this.prev()[0] === 'ASSIGN' && include(HALF_ASSIGNMENTS, tag)) {
-        last = this.tokens.pop();
-        this.tokens.push(['' + tag + "=", '' + tag + "=", last[2]]);
-      } else {
-        this.token(tag, value);
+        return this.tag_half_assignment(tag);
       }
+      this.token(tag, value);
       return true;
     };
     // Token Manipulators
@@ -404,6 +407,13 @@
       indent = (doc.match(HEREDOC_INDENT) || ['']).sort()[0];
       return doc.replace(new RegExp("^" + indent, 'gm'), '').replace(MULTILINER, "\\n").replace(new RegExp(quote, 'g'), '\\"');
     };
+    // Tag a half assignment.
+    Lexer.prototype.tag_half_assignment = function tag_half_assignment(tag) {
+      var last;
+      last = this.tokens.pop();
+      this.tokens.push(['' + tag + "=", '' + tag + "=", last[2]]);
+      return true;
+    };
     // A source of ambiguity in our grammar used to be parameter lists in function
     // definitions versus argument lists in function calls. Walk backwards, tagging
     // parameters specially in order to make things easier for the parser.
diff --git a/src/lexer.coffee b/src/lexer.coffee
index 2efe14f4..e650551e 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -100,7 +100,9 @@ exports.Lexer: class Lexer
     @identifier_error id      if include RESERVED, id
     tag: 'LEADING_WHEN'       if tag is 'WHEN' and include LINE_BREAK, @tag()
     @i += id.length
-    tag: id: CONVERSIONS[id]  if not accessed and include(COFFEE_ALIASES, id)
+    if not accessed
+      tag: id: CONVERSIONS[id]         if include COFFEE_ALIASES, id
+      return @tag_half_assignment(tag) if @prev() and @prev()[0] is 'ASSIGN' and include HALF_ASSIGNMENTS, tag
     @token(tag, id)
     true
 
@@ -270,11 +272,8 @@ exports.Lexer: class Lexer
       tag: 'CALL_START'  if value is '('
       tag: 'INDEX_START' if value is '['
     @i += value.length
-    if space and prev_spaced and @prev()[0] is 'ASSIGN' and include HALF_ASSIGNMENTS, tag
-      last: @tokens.pop()
-      @tokens.push ["$tag=", "$tag=", last[2]]
-    else
-      @token tag, value
+    return @tag_half_assignment(tag) if space and prev_spaced and @prev()[0] is 'ASSIGN' and include HALF_ASSIGNMENTS, tag
+    @token tag, value
     true
 
   # Token Manipulators
@@ -299,6 +298,12 @@ exports.Lexer: class Lexer
        .replace(MULTILINER, "\\n")
        .replace(new RegExp(quote, 'g'), '\\"')
 
+  # Tag a half assignment.
+  tag_half_assignment: (tag) ->
+    last: @tokens.pop()
+    @tokens.push ["$tag=", "$tag=", last[2]]
+    true
+
   # A source of ambiguity in our grammar used to be parameter lists in function
   # definitions versus argument lists in function calls. Walk backwards, tagging
   # parameters specially in order to make things easier for the parser.
diff --git a/test/test_half_assignments.coffee b/test/test_half_assignments.coffee
new file mode 100644
index 00000000..6752b3ae
--- /dev/null
+++ b/test/test_half_assignments.coffee
@@ -0,0 +1,36 @@
+num: 10
+num: - 5
+
+ok num is 5
+
+num: -3
+
+ok num is -3
+
+num: +3
+
+ok num is 3
+
+num: * 10
+
+ok num is 30
+
+num: / 10
+
+ok num is 3
+
+
+val: false
+val: or 'value'
+
+ok val is 'value'
+
+val: and 'other'
+
+ok val is 'other'
+
+
+val: null
+val: ? 'value'
+
+ok val is 'value'
\ No newline at end of file