diff --git a/src/lang/tokeniser.test.ts b/src/lang/tokeniser.test.ts
index b2fb9a09c..402f6edc3 100644
--- a/src/lang/tokeniser.test.ts
+++ b/src/lang/tokeniser.test.ts
@@ -18,7 +18,10 @@ describe('testing helpers', () => {
     expect(isNumber('5?')).toBe(true)
     expect(isNumber('5 + 6')).toBe(true)
     expect(isNumber('5 + a')).toBe(true)
-
+    expect(isNumber('-5')).toBe(true)
+    expect(isNumber('5.5')).toBe(true)
+    expect(isNumber('-5.5')).toBe(true)
+    
     expect(isNumber('a')).toBe(false)
     expect(isNumber('?')).toBe(false)
     expect(isNumber('?5')).toBe(false)
@@ -258,6 +261,46 @@ describe('testing lexer', () => {
       "brace        '}'        from 35  to 36",
     ])
   })
+  it('test negative and decimal numbers', () => {
+    expect(stringSummaryLexer('-1')).toEqual([
+      "number       '-1'       from 0   to 2",
+    ])
+    expect(stringSummaryLexer('-1.5')).toEqual([
+      "number       '-1.5'     from 0   to 4",
+    ])
+    expect(stringSummaryLexer('1.5')).toEqual([
+      "number       '1.5'      from 0   to 3",
+    ])
+    expect(stringSummaryLexer('1.5 + 2.5')).toEqual([
+      "number       '1.5'      from 0   to 3",
+      "whitespace   ' '        from 3   to 4",
+      "operator     '+'        from 4   to 5",
+      "whitespace   ' '        from 5   to 6",
+      "number       '2.5'      from 6   to 9",
+    ])
+    expect(stringSummaryLexer('1.5 - 2.5')).toEqual([
+      "number       '1.5'      from 0   to 3",
+      "whitespace   ' '        from 3   to 4",
+      "operator     '-'        from 4   to 5",
+      "whitespace   ' '        from 5   to 6",
+      "number       '2.5'      from 6   to 9",
+    ])
+    expect(stringSummaryLexer('1.5 + -2.5')).toEqual([
+      "number       '1.5'      from 0   to 3",
+      "whitespace   ' '        from 3   to 4",
+      "operator     '+'        from 4   to 5",
+      "whitespace   ' '        from 5   to 6",
+      "number       '-2.5'     from 6   to 10",
+    ])
+    expect(stringSummaryLexer('-1.5 + 2.5')).toEqual([
+      "number       '-1.5'     from 0   to 4",
+      "whitespace   ' '        from 4   to 5",
+      "operator     '+'        from 5   to 6",
+      "whitespace   ' '        from 6   to 7",
+      "number       '2.5'      from 7   to 10",
+    ])
+
+  })
 })
 
 // helpers
diff --git a/src/lang/tokeniser.ts b/src/lang/tokeniser.ts
index 1181a92e5..7cbcaac6c 100644
--- a/src/lang/tokeniser.ts
+++ b/src/lang/tokeniser.ts
@@ -1,4 +1,6 @@
-const NUMBER = /^[0-9]+/
+// regular expression for number that includes a decimal point or starts with a minus sign
+const NUMBER = /^-?\d+(\.\d+)?/
+
 const WHITESPACE = /\s+/
 const WORD = /^[a-zA-Z_][a-zA-Z0-9_]*/
 // regex that captures everything between two non escaped quotes and the quotes aren't captured in the match
@@ -58,9 +60,6 @@ const makeToken = (
 
 const returnTokenAtIndex = (str: string, startIndex: number): Token | null => {
   const strFromIndex = str.slice(startIndex)
-  if (isOperator(strFromIndex)) {
-    return makeToken('operator', matchFirst(strFromIndex, OPERATOR), startIndex)
-  }
   if (isString(strFromIndex)) {
     return makeToken('string', matchFirst(strFromIndex, STRING), startIndex)
   }
@@ -82,6 +81,9 @@ const returnTokenAtIndex = (str: string, startIndex: number): Token | null => {
   if (isNumber(strFromIndex)) {
     return makeToken('number', matchFirst(strFromIndex, NUMBER), startIndex)
   }
+  if (isOperator(strFromIndex)) {
+    return makeToken('operator', matchFirst(strFromIndex, OPERATOR), startIndex)
+  }
   if (isWord(strFromIndex)) {
     return makeToken('word', matchFirst(strFromIndex, WORD), startIndex)
   }