diff --git a/lib/pure/collections/critbits.nim b/lib/pure/collections/critbits.nim
index 34f5c5470..ed8583ae5 100644
--- a/lib/pure/collections/critbits.nim
+++ b/lib/pure/collections/critbits.nim
@@ -74,11 +74,11 @@ proc rawInsert[T](c: var CritBitTree[T], key: string): Node[T] =
     var newByte = 0
     block blockX:
       while newbyte < key.len:
-        if it.key[newbyte] != key[newbyte]:
+        if newbyte >= it.key.len or it.key[newbyte] != key[newbyte]:
           newotherbits = it.key[newbyte].ord xor key[newbyte].ord
           break blockX
         inc newbyte
-      if it.key[newbyte] != '\0':
+      if newbyte < it.key.len:
         newotherbits = it.key[newbyte].ord
       else:
         return it
diff --git a/lib/pure/ospaths.nim b/lib/pure/ospaths.nim
index 0d638abb9..aeb4a149e 100644
--- a/lib/pure/ospaths.nim
+++ b/lib/pure/ospaths.nim
@@ -196,7 +196,7 @@ proc joinPath*(head, tail: string): string {.
     else:
       result = head & tail
   else:
-    if tail[0] in {DirSep, AltSep}:
+    if tail.len > 0 and tail[0] in {DirSep, AltSep}:
       result = head & tail
     else:
       result = head & DirSep & tail