diff --git a/test-linuxcnc-rs274-native.sh b/test-linuxcnc-rs274-native.sh
index af2ce64..a3bd422 100755
--- a/test-linuxcnc-rs274-native.sh
+++ b/test-linuxcnc-rs274-native.sh
@@ -44,6 +44,7 @@ base_var_file="$build_dir/rs274ngc-base.var"
 ini_named_parameter_file="$(pwd)/tests/gcode/linuxcnc_ini_named_parameter.ini"
 disable_g92_persistence_ini_file="$(pwd)/tests/gcode/linuxcnc_disable_g92_persistence.ini"
 disable_fanuc_style_sub_ini_file="$(pwd)/tests/gcode/linuxcnc_disable_fanuc_style_sub.ini"
+tight_arc_center_tolerance_ini_file="$(pwd)/tests/gcode/linuxcnc_tight_arc_center_tolerance.ini"
 output_dir="$build_dir/outputs"
 mkdir -p "$output_dir"
 cp "$linuxcnc_root/tests/halui/jogging/sim.var" "$base_var_file"
@@ -688,6 +689,15 @@ CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linux
 # passes unit-specific center-arc tolerance to src/emc/rs274ngc/interp_arc.cc
 # arc_data_ijk(), which rejects excessive start/end radius mismatch.
 CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_arc_center_tolerance_good_imperial.ngc >"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_good_imperial.json"
+CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc >"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_default.json"
+if INI_FILE_NAME="$tight_arc_center_tolerance_ini_file" CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_ini.json" 2>"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_ini.err"; then
+    echo "expected linuxcnc_arc_center_tolerance_tight_metric.ngc to fail with tight INI tolerance" >&2
+    exit 1
+fi
+grep -Fq "Radius to end of arc differs from radius to start" \
+    "$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_ini.err"
 if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_arc_center_tolerance_bad_metric.ngc \
     >"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_bad_metric.json" 2>"$output_dir/cnc_sim_linuxcnc_arc_center_tolerance_bad_metric.err"; then
@@ -2053,6 +2063,15 @@ if not any(
 ):
     raise SystemExit("missing LinuxCNC small imperial center-format arc within tolerance")
 
+arc_center_tolerance_tight_metric_default = load("cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_default.json")
+if not any(
+    event["type"] == "arc-feed" and
+    event["line"] == 5 and
+    event["end"]["x"] == 2
+    for event in arc_center_tolerance_tight_metric_default
+):
+    raise SystemExit("missing LinuxCNC metric center-format arc under default tolerance")
+
 incremental_r_arc = load("cnc_sim_linuxcnc_incremental_and_r_arc.json")
 if not any(
     event["type"] == "linear-feed" and
@@ -3010,6 +3029,8 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_extended_plane_cycle.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_arc_planes.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_arc_distance_modes.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_good_imperial.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_default.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_arc_center_tolerance_tight_metric_ini.err"
 echo "dumped $output_dir/cnc_sim_linuxcnc_predefined_positions.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_machine_coordinates.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_cutter_comp.json"
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 9657eb9..546e2ad 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -177,6 +177,7 @@ base_var_file="$build_dir/rs274ngc-source-base.var"
 ini_named_parameter_file="$(pwd)/tests/gcode/linuxcnc_ini_named_parameter.ini"
 disable_g92_persistence_ini_file="$(pwd)/tests/gcode/linuxcnc_disable_g92_persistence.ini"
 disable_fanuc_style_sub_ini_file="$(pwd)/tests/gcode/linuxcnc_disable_fanuc_style_sub.ini"
+tight_arc_center_tolerance_ini_file="$(pwd)/tests/gcode/linuxcnc_tight_arc_center_tolerance.ini"
 multi_spindle_modes_file="$(pwd)/tests/gcode/linuxcnc_multi_spindle_modes.ini"
 multi_spindle_override_file="$(pwd)/tests/gcode/linuxcnc_multi_spindle_override.ini"
 multi_spindle_threading_file="$(pwd)/tests/gcode/linuxcnc_multi_spindle_threading.ini"
@@ -1719,6 +1720,17 @@ CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_arc_center_tolerance_good_imperial.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_good_imperial.json"
+CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_default.json"
+if INI_FILE_NAME="$tight_arc_center_tolerance_ini_file" CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
+    "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc \
+    >"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_ini.json" 2>"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_ini.err"; then
+    echo "expected linuxcnc_arc_center_tolerance_tight_metric.ngc to fail with tight INI tolerance" >&2
+    exit 1
+fi
+grep -Fq "Radius to end of arc differs from radius to start" \
+    "$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_ini.err"
 if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_arc_center_tolerance_bad_metric.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_bad_metric.json" 2>"$output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_bad_metric.err"; then
@@ -3530,6 +3542,15 @@ if not any(
 ):
     raise SystemExit("missing source-linked small imperial center-format arc within tolerance")
 
+arc_center_tolerance_tight_metric_default = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_default.json").read_text())
+if not any(
+    event["type"] == "arc-feed" and
+    event["line"] == 5 and
+    event["end"]["x"] == 2
+    for event in arc_center_tolerance_tight_metric_default
+):
+    raise SystemExit("missing source-linked metric center-format arc under default tolerance")
+
 g76only = json.loads((OUTPUT_DIR / "cnc_sim_linuxcnc_source_g76only.json").read_text())
 if not any(
     event["type"] == "comment" and
@@ -4056,6 +4077,8 @@ echo "dumped $output_dir/cnc_sim_linuxcnc_source_parameter_expression_assignment
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_word_bracket_whitespace.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_m98_mixed_styles_variables.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_good_imperial.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_default.json"
+echo "dumped $output_dir/cnc_sim_linuxcnc_source_arc_center_tolerance_tight_metric_ini.err"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_g76only.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_numbered_parameters.json"
 echo "dumped $output_dir/cnc_sim_linuxcnc_source_rotary_probe_numbered_parameters.json"
diff --git a/tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc b/tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc
new file mode 100644
index 0000000..be68f5f
--- /dev/null
+++ b/tests/gcode/linuxcnc_arc_center_tolerance_tight_metric.ngc
@@ -0,0 +1,6 @@
+G21
+F1
+G0 X0 Y0 Z0
+(Source basis: LinuxCNC src/emc/rs274ngc/rs274ngc_pre.cc applies CENTER_ARC_RADIUS_TOLERANCE_MM from INI before interp_arc.cc checks IJK radius mismatch.)
+G2 X2 Y0 I[1 - 0.0011]
+M2
diff --git a/tests/gcode/linuxcnc_tight_arc_center_tolerance.ini b/tests/gcode/linuxcnc_tight_arc_center_tolerance.ini
new file mode 100644
index 0000000..019a6b0
--- /dev/null
+++ b/tests/gcode/linuxcnc_tight_arc_center_tolerance.ini
@@ -0,0 +1,2 @@
+[RS274NGC]
+CENTER_ARC_RADIUS_TOLERANCE_MM = 0.001