diff --git a/ql/src/codeql_ruby/controlflow/internal/ControlFlowGraphImpl.qll b/ql/src/codeql_ruby/controlflow/internal/ControlFlowGraphImpl.qll
index 759c710f2d0..39a62fcee08 100644
--- a/ql/src/codeql_ruby/controlflow/internal/ControlFlowGraphImpl.qll
+++ b/ql/src/codeql_ruby/controlflow/internal/ControlFlowGraphImpl.qll
@@ -782,12 +782,8 @@ module Trees {
 
     final override predicate succ(AstNode pred, AstNode succ, Completion c) {
       succ = this and
-      (
-        last(operand, pred, c.(BooleanCompletion).getDual())
-        or
-        last(operand, pred, c) and
-        c instanceof SimpleCompletion
-      )
+      last(operand, pred, c) and
+      c instanceof NormalCompletion
     }
   }
 
diff --git a/ql/test/library-tests/controlflow/graph/Cfg.expected b/ql/test/library-tests/controlflow/graph/Cfg.expected
index 8c8ea06a75c..43788edcec7 100644
--- a/ql/test/library-tests/controlflow/graph/Cfg.expected
+++ b/ql/test/library-tests/controlflow/graph/Cfg.expected
@@ -103,6 +103,9 @@ ifs.rb:
 #   36| enter conditional_method_def
 #-----|  -> puts
 
+#   40| enter constant_condition
+#-----|  -> true
+
 loops.rb:
 #    1| enter top-level
 #-----|  -> m1
@@ -2440,7 +2443,7 @@ ifs.rb:
 #-----|  -> If
 
 #   36| UnlessModifier
-#-----|  -> exit top-level (normal)
+#-----|  -> constant_condition
 
 #   36| Method
 #-----|  -> UnlessModifier
@@ -2467,6 +2470,21 @@ ifs.rb:
 #   38| 2
 #-----|  -> Binary
 
+#   40| Method
+#-----|  -> exit top-level (normal)
+
+#   40| constant_condition
+#-----|  -> Method
+
+#   41| If
+#-----|  -> exit constant_condition (normal)
+
+#   41| [false] Unary
+#-----| false -> If
+
+#   41| true
+#-----| true -> [false] Unary
+
 loops.rb:
 #    1| Method
 #-----|  -> m2
@@ -3771,6 +3789,8 @@ ifs.rb:
 
 #   36| exit conditional_method_def
 
+#   40| exit constant_condition
+
 loops.rb:
 #    1| exit top-level
 
@@ -3926,6 +3946,9 @@ ifs.rb:
 #   36| exit conditional_method_def (normal)
 #-----|  -> exit conditional_method_def
 
+#   40| exit constant_condition (normal)
+#-----|  -> exit constant_condition
+
 loops.rb:
 #    1| exit top-level (normal)
 #-----|  -> exit top-level
diff --git a/ql/test/library-tests/controlflow/graph/ifs.rb b/ql/test/library-tests/controlflow/graph/ifs.rb
index a774f1e8ca6..aa8ac8a342b 100644
--- a/ql/test/library-tests/controlflow/graph/ifs.rb
+++ b/ql/test/library-tests/controlflow/graph/ifs.rb
@@ -36,3 +36,9 @@ end
 def conditional_method_def()
   puts "bla"
 end unless 1 == 2
+
+def constant_condition()
+  if !true
+    puts "Impossible"
+  end
+end