diff --git a/lexer/src/chars.rs b/lexer/src/chars.rs
index 8aa2e2c..70be6c7 100644
--- a/lexer/src/chars.rs
+++ b/lexer/src/chars.rs
@@ -33,7 +33,7 @@ impl Lexable for char {
     }
 
     fn is_identifier_initial(&self) -> bool {
-        self.is_alphabetic() || self.is_special_initial()
+        self.is_alphabetic() || self.is_special_initial() || self.is_explicit_sign()
     }
 
     fn is_identifier_subsequent(&self) -> bool {
diff --git a/lexer/tests/expressions.rs b/lexer/tests/expressions.rs
new file mode 100644
index 0000000..1ee9712
--- /dev/null
+++ b/lexer/tests/expressions.rs
@@ -0,0 +1,29 @@
+/* lexer/tests/expressions.rs
+ * Eryn Wells <eryn@erynwells.me>
+ */
+
+extern crate sibillexer;
+
+use sibillexer::{Lexer, Lex, Token};
+
+#[test]
+fn addition() {
+    let mut lex = Lexer::new("(+ 3 4)".chars());
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::LeftParen, "(", 0, 0))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Id, "+", 0, 1))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Num(3), "3", 0, 3))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Num(4), "4", 0, 5))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::RightParen, ")", 0, 6))));
+    assert_eq!(lex.next(), None);
+}
+
+#[test]
+fn subtraction() {
+    let mut lex = Lexer::new("(- 3 4)".chars());
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::LeftParen, "(", 0, 0))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Id, "-", 0, 1))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Num(3), "3", 0, 3))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::Num(4), "4", 0, 5))));
+    assert_eq!(lex.next(), Some(Ok(Lex::new(Token::RightParen, ")", 0, 6))));
+    assert_eq!(lex.next(), None);
+}