diff --git a/src/ocrmypdf/_validation.py b/src/ocrmypdf/_validation.py
index 3a611274..6dc0566b 100644
--- a/src/ocrmypdf/_validation.py
+++ b/src/ocrmypdf/_validation.py
@@ -52,17 +52,6 @@ def check_options_languages(
         system_lang = locale.getlocale()[0]
         if system_lang and not system_lang.startswith('en'):
             log.debug("No language specified; assuming --language %s", DEFAULT_LANGUAGE)
-    DENIED_LANGUAGES = {'equ', 'osd'}
-    if DENIED_LANGUAGES & set(options.languages):
-        log.warning(
-            "The following languages for Tesseract's internal use and should not "
-            "be issued explicitly: "
-            f"{', '.join(DENIED_LANGUAGES)}\n"
-            "OCRmyPDF will ignore them."
-        )
-        options.languages = [
-            lang for lang in options.languages if lang not in DENIED_LANGUAGES
-        ]
     if not ocr_engine_languages:
         return
 
diff --git a/src/ocrmypdf/builtin_plugins/tesseract_ocr.py b/src/ocrmypdf/builtin_plugins/tesseract_ocr.py
index 3d6fc212..ae0f0763 100644
--- a/src/ocrmypdf/builtin_plugins/tesseract_ocr.py
+++ b/src/ocrmypdf/builtin_plugins/tesseract_ocr.py
@@ -14,6 +14,7 @@ from ocrmypdf import hookimpl
 from ocrmypdf._exec import tesseract
 from ocrmypdf._jobcontext import PageContext
 from ocrmypdf.cli import numeric, str_to_int
+from ocrmypdf.exceptions import BadArgsError
 from ocrmypdf.helpers import clamp
 from ocrmypdf.imageops import calculate_downsample, downsample_image
 from ocrmypdf.pluginspec import OcrEngine
@@ -164,6 +165,14 @@ def check_options(options):
             "The --tesseract-pagesegmode argument you select will disable OCR. "
             "This may cause processing to fail."
         )
+    DENIED_LANGUAGES = {'equ', 'osd'}
+    if DENIED_LANGUAGES & set(options.languages):
+        raise BadArgsError(
+            "The following languages for Tesseract's internal use and should not "
+            "be issued explicitly: "
+            f"{', '.join(DENIED_LANGUAGES & set(options.languages))}\n"
+            "Remove them from the -l/--language argument."
+        )
 
 
 @hookimpl
diff --git a/tests/test_tesseract.py b/tests/test_tesseract.py
index 74552db9..0132795f 100644
--- a/tests/test_tesseract.py
+++ b/tests/test_tesseract.py
@@ -13,9 +13,9 @@ import pytest
 
 from ocrmypdf import pdfinfo
 from ocrmypdf._exec import tesseract
-from ocrmypdf.exceptions import MissingDependencyError
+from ocrmypdf.exceptions import BadArgsError, ExitCode, MissingDependencyError
 
-from .conftest import check_ocrmypdf
+from .conftest import check_ocrmypdf, run_ocrmypdf_api
 
 # pylint: disable=redefined-outer-name
 
@@ -144,3 +144,10 @@ def test_tesseract_log_output_raises(caplog):
     with pytest.raises(tesseract.TesseractConfigError):
         tesseract.tesseract_log_output(b'parameter not found: moo')
     assert 'not found' in caplog.text
+
+
+def test_blocked_language(resources, no_outpdf):
+    infile = resources / 'masks.pdf'
+    for bad_lang in ['osd', 'equ']:
+        with pytest.raises(BadArgsError):
+            run_ocrmypdf_api(infile, no_outpdf, '-l', bad_lang)