diff --git a/homeassistant/components/mold_indicator/config_flow.py b/homeassistant/components/mold_indicator/config_flow.py
index ac85d7cc100..96ccbe2f8ee 100644
--- a/homeassistant/components/mold_indicator/config_flow.py
+++ b/homeassistant/components/mold_indicator/config_flow.py
@@ -12,6 +12,7 @@ from homeassistant.const import CONF_NAME, Platform
 from homeassistant.helpers.schema_config_entry_flow import (
     SchemaCommonFlowHandler,
     SchemaConfigFlowHandler,
+    SchemaFlowError,
     SchemaFlowFormStep,
 )
 from homeassistant.helpers.selector import (
@@ -33,11 +34,13 @@ from .const import (
 )
 
 
-async def validate_duplicate(
+async def validate_input(
     handler: SchemaCommonFlowHandler, user_input: dict[str, Any]
 ) -> dict[str, Any]:
     """Validate already existing entry."""
     handler.parent_handler._async_abort_entries_match({**handler.options, **user_input})  # noqa: SLF001
+    if user_input[CONF_CALIBRATION_FACTOR] == 0.0:
+        raise SchemaFlowError("calibration_is_zero")
     return user_input
 
 
@@ -74,13 +77,13 @@ DATA_SCHEMA_CONFIG = vol.Schema(
 CONFIG_FLOW = {
     "user": SchemaFlowFormStep(
         schema=DATA_SCHEMA_CONFIG,
-        validate_user_input=validate_duplicate,
+        validate_user_input=validate_input,
     ),
 }
 OPTIONS_FLOW = {
     "init": SchemaFlowFormStep(
         DATA_SCHEMA_OPTIONS,
-        validate_user_input=validate_duplicate,
+        validate_user_input=validate_input,
     )
 }
 
diff --git a/homeassistant/components/mold_indicator/strings.json b/homeassistant/components/mold_indicator/strings.json
index 2e34bcc1ba1..03c6a05546f 100644
--- a/homeassistant/components/mold_indicator/strings.json
+++ b/homeassistant/components/mold_indicator/strings.json
@@ -3,6 +3,9 @@
     "abort": {
       "already_configured": "[%key:common::config_flow::abort::already_configured_device%]"
     },
+    "error": {
+      "calibration_is_zero": "Calibration factor can't be zero."
+    },
     "step": {
       "user": {
         "description": "Add Mold indicator helper",
@@ -27,6 +30,9 @@
     "abort": {
       "already_configured": "[%key:common::config_flow::abort::already_configured_device%]"
     },
+    "error": {
+      "calibration_is_zero": "Calibration factor can't be zero."
+    },
     "step": {
       "init": {
         "description": "Adjust the calibration factor as required",
diff --git a/tests/components/mold_indicator/test_config_flow.py b/tests/components/mold_indicator/test_config_flow.py
index 7a766be11f5..339cb3a02e7 100644
--- a/tests/components/mold_indicator/test_config_flow.py
+++ b/tests/components/mold_indicator/test_config_flow.py
@@ -89,6 +89,52 @@ async def test_options_flow(hass: HomeAssistant, loaded_entry: MockConfigEntry)
     assert state is not None
 
 
+async def test_calibration_factor_not_zero(hass: HomeAssistant) -> None:
+    """Test calibration factor is not zero."""
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": SOURCE_USER}
+    )
+    assert result["step_id"] == "user"
+    assert result["type"] is FlowResultType.FORM
+
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"],
+        {
+            CONF_NAME: DEFAULT_NAME,
+            CONF_INDOOR_TEMP: "sensor.indoor_temp",
+            CONF_INDOOR_HUMIDITY: "sensor.indoor_humidity",
+            CONF_OUTDOOR_TEMP: "sensor.outdoor_temp",
+            CONF_CALIBRATION_FACTOR: 0.0,
+        },
+    )
+    await hass.async_block_till_done()
+
+    assert result["type"] is FlowResultType.FORM
+    assert result["errors"] == {"base": "calibration_is_zero"}
+
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"],
+        {
+            CONF_NAME: DEFAULT_NAME,
+            CONF_INDOOR_TEMP: "sensor.indoor_temp",
+            CONF_INDOOR_HUMIDITY: "sensor.indoor_humidity",
+            CONF_OUTDOOR_TEMP: "sensor.outdoor_temp",
+            CONF_CALIBRATION_FACTOR: 1.0,
+        },
+    )
+    await hass.async_block_till_done()
+
+    assert result["type"] is FlowResultType.CREATE_ENTRY
+    assert result["options"] == {
+        CONF_NAME: DEFAULT_NAME,
+        CONF_INDOOR_TEMP: "sensor.indoor_temp",
+        CONF_INDOOR_HUMIDITY: "sensor.indoor_humidity",
+        CONF_OUTDOOR_TEMP: "sensor.outdoor_temp",
+        CONF_CALIBRATION_FACTOR: 1.0,
+    }
+
+
 async def test_entry_already_exist(
     hass: HomeAssistant, loaded_entry: MockConfigEntry
 ) -> None: