--- a/Integer.st	Wed Jul 26 12:37:47 2017 +0200
+++ b/Integer.st	Wed Jul 26 12:59:50 2017 +0200
@@ -794,6 +794,8 @@
     "Modified: / 15.11.1999 / 20:35:20 / cg"
 ! !
 
+
+
 !Integer class methodsFor:'class initialization'!
 
 initialize
@@ -850,6 +852,7 @@
     "Modified: 18.7.1996 / 12:26:38 / cg"
 ! !
 
+
 !Integer class methodsFor:'prime numbers'!
 
 flushPrimeCache
@@ -1227,6 +1230,7 @@
     ^ self == Integer
 ! !
 
+
 !Integer methodsFor:'Compatibility-Dolphin'!
 
 highWord
@@ -1476,6 +1480,7 @@
     "
 ! !
 
+
 !Integer methodsFor:'bcd conversion'!
 
 decodeFromBCD
@@ -4783,6 +4788,7 @@
 
 isPrime
     "return true if I am a prime Number.
+     Pre-condition: I am positive.
      This is a q&d hack, which may need optimization if heavily used."
 
     |limit firstFewPrimes|
@@ -4819,6 +4825,12 @@
         ^ PrimeNumberGenerator isPrime:self.
     ].
 
+    "/ Not absolutely correct, but was broken much worse before.
+    limit := self sqrt.
+    limit isNaN ifTrue:[
+        DomainError raiseRequestErrorString:'Number too large for current fallback implementation.'.
+    ].
+    limit := limit asInteger.
     (firstFewPrimes last+2) to:limit by:2 do:[:i |
         (self \\ i) == 0 ifTrue:[ ^ false ].
     ].
@@ -4831,6 +4843,8 @@
      Time millisecondsToRun:[ (1 to:1000000) count:[:n | n isPrime]] 936    with firstFewPrimes (less tests)
      Time millisecondsToRun:[ (1 to:1000000) count:[:n | n isPrime]] 343    with primeCache
     "
+
+    "Modified (comment): / 26-07-2017 / 12:58:45 / mawalch"
 !
 
 nextMultipleOf: n
@@ -4975,6 +4989,7 @@
     "Created: / 09-01-2012 / 17:18:06 / cg"
 ! !
 
+
 !Integer methodsFor:'special modulo arithmetic'!
 
 add_32:anInteger