diff --git a/check/README.md b/check/README.md
index 268d72e9..acb9fa5f 100644
--- a/check/README.md
+++ b/check/README.md
@@ -245,8 +245,8 @@ The following methods are available in Ruby test programs.
   `true` if the FORM job issued the expected warning, otherwise `false`.
 
 The following methods are similar to `warning?`,
-but they check for preprocessor errors, compile-time errors,
-and run-time errors, respectively:
+but they check for preprocessor errors, compile-time errors, run-time errors,
+and internal errors (which should never happen), respectively:
 
 - `preprocess_error? → bool`  
   `preprocess_error?(expected_message : string) → bool`
@@ -254,6 +254,8 @@ and run-time errors, respectively:
   `compile_error?(expected_message : string) → bool`
 - `runtime_error? → bool`  
   `runtime_error?(expected_message : string) → bool`
+- `internal_error? → bool`  
+  `internal_error?(expected_message : string) → bool`
 
 #### Standard streams
 
diff --git a/check/check.rb b/check/check.rb
index 835e5407..0283ba2c 100755
--- a/check/check.rb
+++ b/check/check.rb
@@ -799,10 +799,19 @@ def runtime_error?(expected_message = nil)
     end
   end
 
+  # true if the FORM job reported an internal error, which should never happen.
+  def internal_error?(expected_message = nil)
+    if expected_message.nil?
+      @stdout =~ / ~~> Internal error/
+    else
+      @cleaned_stdout =~ / ~~> Internal error.*#{Regexp.escape(expected_message)}/
+    end
+  end
+
   # true if the FORM job completed without any warnings/errors and
   # the exit code was 0.
   def succeeded?
-    if finished? && !warning? && !preprocess_error? && !compile_error? && !runtime_error? && return_value == 0
+    if finished? && !warning? && !preprocess_error? && !compile_error? && !runtime_error? && !internal_error? && return_value == 0
       if FormTest.cfg.valgrind.nil?
         if @stderr.empty?
           return true