diff --git a/frontend/src/app/util/simple_math.cljs b/frontend/src/app/util/simple_math.cljs
index 45cb01719..c92e8d6de 100644
--- a/frontend/src/app/util/simple_math.cljs
+++ b/frontend/src/app/util/simple_math.cljs
@@ -38,8 +38,8 @@
               second-value (interpret (second args) init-value)]
           (case operator
             "+" (+ init-value second-value)
-            "-" (- init-value second-value)
-            "*" (* init-value second-value)
+            "-" (- 0 second-value)          ;; Note that there is ambiguity, so we don't allow
+            "*" (* init-value second-value) ;; relative substraction, it's only a negative number
             "/" (/ init-value second-value)))
         (let [value (interpret (first args) init-value)]
           (loop [value     value
diff --git a/frontend/tests/app/test_util_simple_math.cljs b/frontend/tests/app/test_util_simple_math.cljs
index 98f73eb1f..bc6d48c74 100644
--- a/frontend/tests/app/test_util_simple_math.cljs
+++ b/frontend/tests/app/test_util_simple_math.cljs
@@ -41,6 +41,10 @@
     (let [result (sm/expr-eval "*10" 20)]
       (t/is (= result 200))))
 
+  (t/testing "Evaluate a negative number (not relative substraction)"
+    (let [result (sm/expr-eval "-10" 20)]
+      (t/is (= result -10))))
+
   (t/testing "Evaluate a relative complex operation"
     (let [result (sm/expr-eval "+(10*2 - 5)" 20)]
       (t/is (= result 35))))
@@ -63,16 +67,19 @@
       (t/is (= result1 result2 12.5))))
 
   (t/testing "Evaluate a relative operation with decimals"
-    (let [result (sm/expr-eval "*.5" 20)]
-      (t/is (= result 10))))
+    (let [result1 (sm/expr-eval "*.5" 20)
+          result2 (sm/expr-eval "*,5" 20)]
+      (t/is (= result1 result2 10))))
 
   (t/testing "Evaluate a percentual operation with decimals"
-    (let [result (sm/expr-eval "+10.5%" 20)]
-      (t/is (= result 22.1))))
+    (let [result1 (sm/expr-eval "+10.5%" 20)
+          result2 (sm/expr-eval "+10,5%" 20)]
+      (t/is (= result1 result2 22.1))))
 
   (t/testing "Evaluate a complex operation with decimals"
-    (let [result (sm/expr-eval "(20.333 + 10%) * (1 / 3)" 20)]
-      (t/is (cm/close? result 7.44433333))))
+    (let [result1 (sm/expr-eval "(20.333 + 10%) * (1 / 3)" 20)
+          result2 (sm/expr-eval "(20,333 + 10%) * (1 / 3)" 20)]
+      (t/is (cm/close? result1 result2 7.44433333))))
 
   )