diff --git a/ShellCheck.cabal b/ShellCheck.cabal
index 8afebe1..1226588 100644
--- a/ShellCheck.cabal
+++ b/ShellCheck.cabal
@@ -54,7 +54,7 @@ library
       containers           >= 0.5.6 && < 0.7,
       deepseq              >= 1.4.1 && < 1.5,
       Diff                 >= 0.4.0 && < 0.5,
-      fgl                  >= 5.7.0 && < 5.8.1.0,
+      fgl                  >= 5.7.0 && < 5.9,
       filepath             >= 1.4.0 && < 1.5,
       mtl                  >= 2.2.2 && < 2.3,
       parsec               >= 3.1.14 && < 3.2,
diff --git a/src/ShellCheck/CFG.hs b/src/ShellCheck/CFG.hs
index e0c6267..ebfeaa0 100644
--- a/src/ShellCheck/CFG.hs
+++ b/src/ShellCheck/CFG.hs
@@ -1301,7 +1301,9 @@ findPostDominators mainexit graph = asArray
     reversed = grev withExitEdges
     postDoms = dom reversed mainexit
     (_, maxNode) = nodeRange graph
-    asArray = array (0, maxNode) postDoms
+    -- Assume everything *not* reachable from 'mainexit' has every
+    -- node as postdominator.
+    asArray = listArray (0, maxNode) (replicate (maxNode+1) (nodes graph)) // postDoms
 
 return []
 runTests =  $( [| $(forAllProperties) (quickCheckWithResult (stdArgs { maxSuccess = 1 }) ) |])