diff --git a/source/ide/ide_methods.bas b/source/ide/ide_methods.bas
index 8f2d6741a..0f17b5ce8 100644
--- a/source/ide/ide_methods.bas
+++ b/source/ide/ide_methods.bas
@@ -19664,10 +19664,11 @@ FUNCTION isnumber (__a$)
     ff = 0
     ee = 0
     dd = 0
+    neg = 0
     FOR i = 1 TO LEN(a$)
         a = ASC(a$, i)
         IF a = 45 THEN
-            IF (i = 1 AND LEN(a$) > 1) OR (i > 1 AND ((dd > 0 AND dd = i - 1) OR (ee > 0 AND ee = i - 1) OR (ff > 0 AND ff = i - 1))) THEN _CONTINUE
+            IF (i = 1 AND LEN(a$) > 1) OR (i > 1 AND ((dd > 0 AND dd = i - 1) OR (ee > 0 AND ee = i - 1) OR (ff > 0 AND ff = i - 1))) THEN neg = (i = 1): _CONTINUE
             EXIT FUNCTION
         END IF
         IF a = 46 THEN
@@ -19678,16 +19679,19 @@ FUNCTION isnumber (__a$)
         IF a = 68 THEN 'dD
             IF dd > 0 OR ee > 0 OR ff > 0 THEN EXIT FUNCTION
             dd = i
+            IF neg <> 0 AND dd = 2 THEN EXIT FUNCTION
             _CONTINUE
         END IF
         IF a = 69 THEN 'eE
             IF dd > 0 OR ee > 0 OR ff > 0 THEN EXIT FUNCTION
             ee = i
+            IF neg <> 0 AND ee = 2 THEN EXIT FUNCTION
             _CONTINUE
         END IF
         IF a = 70 THEN 'fF
             IF dd > 0 OR ee > 0 OR ff > 0 THEN EXIT FUNCTION
             ff = i
+            IF neg <> 0 AND ff = 2 THEN EXIT FUNCTION
             _CONTINUE
         END IF
         IF a = 43 THEN '+