diff --git a/src/cmd/cli_modify.cpp b/src/cmd/cli_modify.cpp
index 6de146ce..27cd8d43 100644
--- a/src/cmd/cli_modify.cpp
+++ b/src/cmd/cli_modify.cpp
@@ -287,7 +287,20 @@ std::function<bool(cli_result_t &)> cli_tool_t::start_modify(json11::Json cfg)
     changer->parent = this;
     changer->image_name = cfg["image"].string_value();
     changer->new_name = cfg["rename"].string_value();
-    changer->new_size = parse_size(cfg["resize"].as_string());
+    if (!cfg["resize"].is_null())
+    {
+        bool ok = false;
+        changer->new_size = parse_size(cfg["resize"].as_string(), &ok);
+        if (!ok)
+        {
+            delete changer;
+            return [size = cfg["resize"].as_string()](cli_result_t & result)
+            {
+                result = (cli_result_t){ .err = EINVAL, .text = "Invalid syntax for size: "+size };
+                return true;
+            };
+        }
+    }
     changer->force_size = cfg["force_size"].bool_value();
     changer->inc_size = cfg["inc_size"].bool_value();
     changer->force = cfg["force"].bool_value();
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index d72fcf78..c40e0d06 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -64,6 +64,8 @@ OLD=1 ./test_move_reappear.sh
 
 ./test_rm.sh
 
+./test_modify_image_resize.sh
+
 ./test_rm_degraded.sh
 
 ./test_snapshot_chain.sh
diff --git a/tests/test_modify_image_resize.sh b/tests/test_modify_image_resize.sh
new file mode 100755
index 00000000..10327813
--- /dev/null
+++ b/tests/test_modify_image_resize.sh
@@ -0,0 +1,28 @@
+#!/bin/bash -ex
+
+# Test that modify refuses an invalid --resize value instead of ignoring it
+
+. `dirname $0`/common.sh
+
+wait_etcd
+
+$ETCDCTL put /vitastor/config/pools '{"1":{"name":"testpool","scheme":"replicated","pg_size":2,"pg_minsize":1,"pg_count":1,"failure_domain":"osd"}}'
+
+$VITASTOR_CLI create -s 1G --pool testpool testimg
+
+for size in 1.5G 10X abc ''; do
+    r=0
+    $VITASTOR_CLI modify testimg --resize "$size" || r=$?
+    if [[ $r != 22 ]]; then
+        format_error "modify --resize '$size' should fail with EINVAL (22), but exited with $r"
+    fi
+done
+
+$ETCDCTL get --print-value-only /vitastor/config/inode/1/1 | jq -e '.size == 1073741824' || \
+    format_error "Image size should stay 1G after refused resizes"
+
+$VITASTOR_CLI modify testimg --resize 2G
+$ETCDCTL get --print-value-only /vitastor/config/inode/1/1 | jq -e '.size == 2147483648' || \
+    format_error "Image size should be 2G after --resize 2G"
+
+format_green OK