diff --git a/src/lexer/errors.rs b/src/lexer/errors.rs
index a08118c..457fe14 100644
--- a/src/lexer/errors.rs
+++ b/src/lexer/errors.rs
@@ -2,9 +2,9 @@ use thiserror::Error;
 
 #[derive(Error, Debug)]
 pub enum LexerErrors {
-    #[error("unexpected character {char} at position {pos}")]
-    UnexpectedCharacter {
-        char: char,
+    #[error("unexpected character {token} at position {pos}")]
+    InvalidTokenError {
+        token: String,
         pos: usize,
     },
     #[error("cannot lex an empty text sequence")]
diff --git a/src/lexer/mod.rs b/src/lexer/mod.rs
index 988871c..b238760 100644
--- a/src/lexer/mod.rs
+++ b/src/lexer/mod.rs
@@ -19,10 +19,10 @@ pub type Result<T> = std::result::Result<T, errors::LexerErrors>;
 pub struct Lexer {
     input: Vec<char>,
     pos: usize,
+    read_pointer: usize,
 }
 
 
-
 impl Lexer {
     /// Create a new Lexer for the given String
     /// Example:
@@ -33,18 +33,30 @@ impl Lexer {
     /// ```
     #[inline]
     pub fn new(input: &str) -> Lexer {
-        Lexer { input: input.chars().collect(), pos: 0 }
+        Lexer { input: input.chars().collect(), pos: 0, read_pointer: 0 }
     }
 
     // Get the next token
     pub fn next(&mut self) -> Result<Option<Token>> {
         if let Some((fsm, cbuf)) = self.longest_token_prefix() {
-            if let Some(token) = fsm::get_token(&fsm, &cbuf, TokenMeta{ pos: self.pos }) {
-                self.pos += cbuf.len();
+            if let Some(token) = fsm::get_token(&fsm, &cbuf, TokenMeta { pos: self.pos }) {
+                // if a token could be derived
+                self.pos = self.read_pointer;
                 Ok(Some(token))
             } else {
-                // TODO: handling of end of stream
-                Err(LexerErrors::UnexpectedCharacter { char: self.input.get(self.pos), pos: self.pos })
+                // If no token could be found
+                if self.input.len() > self.read_pointer {
+                    // If not at the end of the input
+                    Err(LexerErrors::InvalidTokenError {
+                        token: self.input.get(self.pos..).unwrap()
+                            .iter()
+                            .take(5)
+                            .collect(),
+                        pos: self.pos })
+                } else {
+                    // If at the end of the input
+                    Ok(None)
+                }
             }
         } else {
             // if no more tokens are there
@@ -66,14 +78,15 @@ impl Lexer {
                 cbuf.push(*cur);
             } else if fsm.is_error() {
                 fsm.revert();
-                break
+                break;
             }
+            self.read_pointer += 1;
         }
         Some((fsm, cbuf))
     }
-
 }
 
+#[warn(dead_code)]
 #[cfg(test)]
 mod test {
     use super::*;
@@ -94,7 +107,6 @@ mod test {
         assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 12 }, OpType::MUL)))));
         assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 13 }, 60.0)))));
         assert!(matches!(lexer.next(), Ok(Some(Token::CBR(TokenMeta { pos: 15 })))));
-        // println!("{:?}", lexer.next());
         assert!(matches!(lexer.next(), Ok(None)));
     }
 
@@ -103,6 +115,25 @@ mod test {
         let mut lexer = Lexer::new("15+@");
         assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta{ pos: 0 }, 15.0)))));
         assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta{ pos: 2 }, OpType::ADD)))));
-        assert!(matches!(lexer.next(), Err(LexerErrors::UnexpectedCharacter { char: _, pos: _ })))
+        assert!(matches!(lexer.next(), Err(LexerErrors::InvalidTokenError { token: _, pos: _ })))
     }
-}
+
+    #[test]
+    fn spaces_are_ignored() {
+        let mut lexer = Lexer::new("  15 / 3  ^ 2 +     20 -(    5  * 60   )  ");
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 0 }, 15.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 4 }, OpType::DIV)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 6 }, 3.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 8 }, OpType::POW)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 11 }, 2.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 13},  OpType::ADD)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 15 }, 20.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 22 }, OpType::SUB)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OBR(TokenMeta { pos: 24 })))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 25 }, 5.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::OP(TokenMeta { pos: 30 }, OpType::MUL)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::ID(TokenMeta { pos: 33 }, 60.0)))));
+        assert!(matches!(lexer.next(), Ok(Some(Token::CBR(TokenMeta { pos: 36 })))));
+        assert!(matches!(lexer.next(), Ok(None)));
+    }
+        }