diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index 7e3c139..911274b 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -289,6 +289,27 @@ CNC_SIM_RS274_VAR="$var_file" \
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_dynamic_tool_length.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_dynamic_tool_length.json"
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc
+# convert_tool_length_offset() rejects invalid G43.2 H/axis combinations,
+# and src/emc/rs274ngc/interp_find.cc find_tool_index() rejects H tool
+# numbers missing from the LinuxCNC tooldata table.
+tool_length_offset_error_cases=(
+    "linuxcnc_g43_missing_tool_error|Requested tool 99 not found in the tool table"
+    "linuxcnc_g43_2_missing_tool_error|Requested tool 99 not found in the tool table"
+    "linuxcnc_g43_2_h_axis_error|G43.2: Can not have both H and axis words"
+    "linuxcnc_g43_2_missing_h_axis_error|G43.2: No axes specified and H word missing"
+)
+for case in "${tool_length_offset_error_cases[@]}"; do
+    fixture=${case%%|*}
+    expected=${case#*|}
+    if CNC_SIM_RS274_VAR="$var_file" \
+        "$build_dir/linuxcnc_rs274_source_dump" "tests/gcode/$fixture.ngc" \
+        >"$output_dir/cnc_sim_linuxcnc_source_$fixture.json" 2>"$output_dir/cnc_sim_linuxcnc_source_$fixture.err"; then
+        echo "expected $fixture.ngc to fail" >&2
+        exit 1
+    fi
+    grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
+done
 CNC_SIM_RS274_VAR="$var_file" \
     "$build_dir/linuxcnc_rs274_source_dump" tests/gcode/linuxcnc_canned_cycle.ngc \
     >"$output_dir/cnc_sim_linuxcnc_source_canned_cycle.json"
diff --git a/test-native.sh b/test-native.sh
index 12b4dc5..506187a 100755
--- a/test-native.sh
+++ b/test-native.sh
@@ -145,6 +145,8 @@ grep -F 'convert_lathe_diameter_mode() scales G7/G8 X words and G76 I/J/K words'
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_mode.ngc' docs/linuxcnc-porting.md >/dev/null
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_g76.ngc' docs/linuxcnc-porting.md >/dev/null
 grep -F 'missing source-linked G7 diameter-mode G76 final threading pass' test-linuxcnc-source-link.sh >/dev/null
+grep -F 'convert_tool_length_offset() rejects invalid G43.2 H/axis combinations' test-linuxcnc-source-link.sh >/dev/null
+grep -F 'linuxcnc_g43_2_missing_h_axis_error|G43.2: No axes specified and H word missing' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'read_atsign()' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_polar_coordinates.ngc' test-linuxcnc-source-link.sh >/dev/null
 grep -F 'tests/gcode/linuxcnc_polar_coordinate_variants.ngc' test-linuxcnc-source-link.sh >/dev/null
diff --git a/tests/gcode/linuxcnc_g43_2_h_axis_error.ngc b/tests/gcode/linuxcnc_g43_2_h_axis_error.ngc
new file mode 100644
index 0000000..b07e0a2
--- /dev/null
+++ b/tests/gcode/linuxcnc_g43_2_h_axis_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 G17
+G43.2 H1 X1
+M30
diff --git a/tests/gcode/linuxcnc_g43_2_missing_h_axis_error.ngc b/tests/gcode/linuxcnc_g43_2_missing_h_axis_error.ngc
new file mode 100644
index 0000000..8f2e1e3
--- /dev/null
+++ b/tests/gcode/linuxcnc_g43_2_missing_h_axis_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 G17
+G43.2
+M30
diff --git a/tests/gcode/linuxcnc_g43_2_missing_tool_error.ngc b/tests/gcode/linuxcnc_g43_2_missing_tool_error.ngc
new file mode 100644
index 0000000..a6b48da
--- /dev/null
+++ b/tests/gcode/linuxcnc_g43_2_missing_tool_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 G17
+G43.2 H99
+M30
diff --git a/tests/gcode/linuxcnc_g43_missing_tool_error.ngc b/tests/gcode/linuxcnc_g43_missing_tool_error.ngc
new file mode 100644
index 0000000..e3f7c72
--- /dev/null
+++ b/tests/gcode/linuxcnc_g43_missing_tool_error.ngc
@@ -0,0 +1,3 @@
+G21 G90 G17
+G43 H99
+M30