diff --git a/kiplot/out_any_layer.py b/kiplot/out_any_layer.py
index e0953d92..0d342853 100644
--- a/kiplot/out_any_layer.py
+++ b/kiplot/out_any_layer.py
@@ -77,7 +77,8 @@ class AnyLayerOptions(BaseOptions):
             # Plot single layer to file
             logger.debug("Opening plot file for layer `{}` format `{}`".format(l, self._plot_format))
             if not plot_ctrl.OpenPlotfile(suffix, self._plot_format, desc):
-                raise PlotError("OpenPlotfile failed!")
+                # Shouldn't happen
+                raise PlotError("OpenPlotfile failed!")  # pragma: no cover
 
             logger.debug("Plotting layer `{}` to `{}`".format(l, plot_ctrl.GetPlotFileName()))
             plot_ctrl.PlotLayer()
diff --git a/kiplot/pre_base.py b/kiplot/pre_base.py
index 6d67bef4..971dbc14 100644
--- a/kiplot/pre_base.py
+++ b/kiplot/pre_base.py
@@ -70,8 +70,8 @@ class BasePreFlight(object):
     def disable(self):
         self._enabled = False
 
-    def is_enabled(self):
-        return self._enabled
+    # def is_enabled(self):
+    #     return self._enabled
 
     def __str__(self):
         return "{}: {}".format(self._name, self._enabled)
diff --git a/kiplot/pre_drc.py b/kiplot/pre_drc.py
index 56aed63e..7e5c8d6b 100644
--- a/kiplot/pre_drc.py
+++ b/kiplot/pre_drc.py
@@ -41,5 +41,5 @@ class Run_DRC(BasePreFlight):  # noqa: F821
             if ret < 0:
                 logger.error('DRC errors: %d', -ret)
             else:
-                logger.error('DRC returned %d', ret)  # pragma: no cover
+                logger.error('DRC returned %d', ret)
             exit(DRC_ERROR)
diff --git a/tests/test_plot/test_yaml_errors.py b/tests/test_plot/test_yaml_errors.py
index 0cf7cae0..895b8a59 100644
--- a/tests/test_plot/test_yaml_errors.py
+++ b/tests/test_plot/test_yaml_errors.py
@@ -351,6 +351,14 @@ def test_error_wrong_type_4():
     ctx.clean_up()
 
 
+def test_error_wrong_type_5():
+    """ check_zone_fills = number """
+    ctx = context.TestContext('ErrorWrongType5', PRJ, 'error_pre_wrong_type_5', '')
+    ctx.run(EXIT_BAD_CONFIG)
+    assert ctx.search_err("In preflight 'check_zone_fills': must be boolean")
+    ctx.clean_up()
+
+
 def test_error_yaml():
     ctx = context.TestContext('ErrorYAML', PRJ, 'error_yaml', '')
     ctx.run(EXIT_BAD_CONFIG)
@@ -384,3 +392,17 @@ def test_error_bom_wrong_format():
     ctx.run(EXIT_BAD_CONFIG)
     assert ctx.search_err("Option .?format.? must be any of")
     ctx.clean_up()
+
+
+def test_error_gerber_precision():
+    ctx = context.TestContext('GerberPrecisionError', PRJ, 'error_gerber_precision', '')
+    ctx.run(EXIT_BAD_CONFIG)
+    assert ctx.search_err(".?gerber_precision.? must be 4.5 or 4.6")
+    ctx.clean_up()
+
+
+def test_error_wrong_drill_marks():
+    ctx = context.TestContext('WrongDrillMarks', PRJ, 'error_wrong_drill_marks', '')
+    ctx.run(EXIT_BAD_CONFIG)
+    assert ctx.search_err("Unknown drill mark type: bogus")
+    ctx.clean_up()
diff --git a/tests/yaml_samples/error_gerber_precision.kiplot.yaml b/tests/yaml_samples/error_gerber_precision.kiplot.yaml
new file mode 100644
index 00000000..788d953b
--- /dev/null
+++ b/tests/yaml_samples/error_gerber_precision.kiplot.yaml
@@ -0,0 +1,36 @@
+# Example KiPlot config file for a basic 2-layer board
+kiplot:
+  version: 1
+
+outputs:
+
+  - name: 'gerbers'
+    comment: "Gerbers for the Gerber god"
+    type: gerber
+    dir: gerberdir
+    options:
+      # generic layer options
+      exclude_edge_layer: false
+      exclude_pads_from_silkscreen: false
+      use_aux_axis_as_origin: false
+      plot_sheet_reference: false
+      plot_footprint_refs: true
+      plot_footprint_values: true
+      force_plot_invisible_refs_vals: false
+      tent_vias: true
+
+      # gerber options
+      line_width: 0.15
+      subtract_mask_from_silk: true
+      use_protel_extensions: false
+      gerber_precision: 4.7
+      create_gerber_job_file: true
+      use_gerber_x2_attributes: true
+      use_gerber_net_attributes: false
+
+    layers:
+      - layer: F.Cu
+        suffix: F_Cu
+      - layer: F.SilkS
+        suffix: F_SilkS
+
diff --git a/tests/yaml_samples/error_pre_wrong_type_5.kiplot.yaml b/tests/yaml_samples/error_pre_wrong_type_5.kiplot.yaml
new file mode 100644
index 00000000..6edb2f62
--- /dev/null
+++ b/tests/yaml_samples/error_pre_wrong_type_5.kiplot.yaml
@@ -0,0 +1,10 @@
+# Example KiPlot config file
+kiplot:
+  version: 1
+
+preflight:
+  update_xml: true
+  run_erc: true
+  check_zone_fills: Hi!
+
+
diff --git a/tests/yaml_samples/error_wrong_drill_marks.kiplot.yaml b/tests/yaml_samples/error_wrong_drill_marks.kiplot.yaml
new file mode 100644
index 00000000..f5cda614
--- /dev/null
+++ b/tests/yaml_samples/error_wrong_drill_marks.kiplot.yaml
@@ -0,0 +1,30 @@
+kiplot:
+  version: 1
+
+outputs:
+  - name: DXF
+    comment: "DXF files"
+    type: dxf
+    dir: DXF
+    options:
+      exclude_edge_layer: false
+      exclude_pads_from_silkscreen: false
+      use_aux_axis_as_origin: false
+      plot_sheet_reference: false
+      plot_footprint_refs: true
+      plot_footprint_values: true
+      force_plot_invisible_refs_vals: false
+      tent_vias: true
+
+      # DXF options
+      drill_marks: bogus
+      sketch_plot: false
+      use_aux_axis_as_origin: false
+      polygon_mode: true
+      metric_units: false
+    layers:
+      - layer: F.Cu
+        suffix: F_Cu
+      - layer: F.Fab
+        suffix: F_Fab
+