diff --git a/test-linuxcnc-rs274-native.sh b/test-linuxcnc-rs274-native.sh
index f30fb57..9ea8dec 100755
--- a/test-linuxcnc-rs274-native.sh
+++ b/test-linuxcnc-rs274-native.sh
@@ -525,6 +525,25 @@ for case in "${threading_convert_error_cases[@]}"; do
     fi
     grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_$fixture.err"
 done
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc convert_probe()
+# rejects zero feed, feed-per-revolution mode, and degenerate probe moves before
+# issuing STRAIGHT_PROBE().
+probe_convert_error_cases=(
+    "linuxcnc_probe_zero_feed_error|Cannot probe with zero feed rate"
+    "linuxcnc_probe_feed_per_rev_error|Cannot probe with feed per rev mode"
+    "linuxcnc_probe_start_too_close_error|Start point too close to probe point"
+)
+for case in "${probe_convert_error_cases[@]}"; do
+    fixture=${case%%|*}
+    expected=${case#*|}
+    if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$var_file" \
+        "$build_dir/linuxcnc_rs274_dump" "tests/gcode/$fixture.ngc" \
+        >"$output_dir/cnc_sim_linuxcnc_$fixture.json" 2>"$output_dir/cnc_sim_linuxcnc_$fixture.err"; then
+        echo "expected $fixture.ngc to fail" >&2
+        exit 1
+    fi
+    grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_$fixture.err"
+done
 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_threading_sync.ngc >"$output_dir/cnc_sim_linuxcnc_threading_sync.json"
 CNC_SIM_RS274_VAR="$var_file" "$build_dir/linuxcnc_rs274_dump" tests/gcode/linuxcnc_threading_cycle.ngc >"$output_dir/cnc_sim_linuxcnc_threading_cycle.json"
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc
diff --git a/test-linuxcnc-source-link.sh b/test-linuxcnc-source-link.sh
index c026dc5..43cb323 100755
--- a/test-linuxcnc-source-link.sh
+++ b/test-linuxcnc-source-link.sh
@@ -1182,6 +1182,25 @@ for case in "${threading_convert_error_cases[@]}"; do
     fi
     grep -Fq "$expected" "$output_dir/cnc_sim_linuxcnc_source_$fixture.err"
 done
+# Source basis: LinuxCNC src/emc/rs274ngc/interp_convert.cc convert_probe()
+# rejects zero feed, feed-per-revolution mode, and degenerate probe moves before
+# issuing STRAIGHT_PROBE().
+probe_convert_error_cases=(
+    "linuxcnc_probe_zero_feed_error|Cannot probe with zero feed rate"
+    "linuxcnc_probe_feed_per_rev_error|Cannot probe with feed per rev mode"
+    "linuxcnc_probe_start_too_close_error|Start point too close to probe point"
+)
+for case in "${probe_convert_error_cases[@]}"; do
+    fixture=${case%%|*}
+    expected=${case#*|}
+    if CNC_SIM_RS274_FILE_MODE=1 CNC_SIM_RS274_VAR="$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
 # Source basis: LinuxCNC src/emc/rs274ngc/interp_read.cc
 # read_items() only consumes a leading N word before item dispatch;
 # read_one_item() then uses the default reader table from interp_array.cc
diff --git a/tests/gcode/linuxcnc_probe_feed_per_rev_error.ngc b/tests/gcode/linuxcnc_probe_feed_per_rev_error.ngc
new file mode 100644
index 0000000..f09d310
--- /dev/null
+++ b/tests/gcode/linuxcnc_probe_feed_per_rev_error.ngc
@@ -0,0 +1,4 @@
+G21 G90 G17
+G95
+F1
+G38.2 Z1
diff --git a/tests/gcode/linuxcnc_probe_start_too_close_error.ngc b/tests/gcode/linuxcnc_probe_start_too_close_error.ngc
new file mode 100644
index 0000000..360f5fa
--- /dev/null
+++ b/tests/gcode/linuxcnc_probe_start_too_close_error.ngc
@@ -0,0 +1,4 @@
+G21 G90 G17
+G0 Z0
+F100
+G38.2 Z0
diff --git a/tests/gcode/linuxcnc_probe_zero_feed_error.ngc b/tests/gcode/linuxcnc_probe_zero_feed_error.ngc
new file mode 100644
index 0000000..22c9580
--- /dev/null
+++ b/tests/gcode/linuxcnc_probe_zero_feed_error.ngc
@@ -0,0 +1,2 @@
+G21 G90 G17
+G38.2 Z1