diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
index 4add57db345a..c1b3456b7a6d 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java
@@ -33,6 +33,8 @@
 import io.swagger.v3.oas.models.responses.ApiResponses;
 import org.apache.commons.lang3.StringUtils;
 import org.openapitools.codegen.utils.ModelUtils;
+
+import static org.openapitools.codegen.utils.StringUtils.camelize;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -924,13 +926,53 @@ private String uniqueName(final String name) {
         String uniqueName = name;
         int count = 0;
         while (true) {
-            if (!openAPI.getComponents().getSchemas().containsKey(uniqueName) && !uniqueNames.contains(uniqueName)) {
+            if (!isNameTaken(uniqueName)) {
                 return uniqueName;
             }
             uniqueName = name + "_" + ++count;
         }
     }
 
+    /**
+     * Whether the candidate schema name collides with an existing one.
+     *
+     * <p>Names are compared as the default model mangler would emit them, i.e.
+     * {@code camelize(sanitizeName(name))}: the inline body schema {@code importMembers_request} and
+     * a spec-defined {@code ImportMembersRequest} both become the model {@code ImportMembersRequest}.
+     * Comparing the raw keys only, the two look distinct, the inline schema is registered under its
+     * own key, and later one model silently overwrites the other - the properties of the overwritten
+     * model disappear from the generated code. Treating them as a collision yields
+     * {@code importMembers_request_1} instead, so both models survive.
+     *
+     * <p>Mirroring the mangler rather than lowercasing keeps names that really do stay distinct
+     * apart: {@code Importmembersrequest} mangles to itself, not to {@code ImportMembersRequest}.
+     *
+     * @param candidate the candidate name
+     * @return true if the name is already taken
+     */
+    private boolean isNameTaken(final String candidate) {
+        if (openAPI.getComponents().getSchemas().containsKey(candidate) || uniqueNames.contains(candidate)) {
+            return true;
+        }
+
+        String normalized = normalizeNameForCollision(candidate);
+        for (String existing : openAPI.getComponents().getSchemas().keySet()) {
+            if (normalized.equals(normalizeNameForCollision(existing))) {
+                return true;
+            }
+        }
+        for (String existing : uniqueNames) {
+            if (normalized.equals(normalizeNameForCollision(existing))) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private String normalizeNameForCollision(final String name) {
+        return camelize(sanitizeName(name));
+    }
+
     private void flattenProperties(OpenAPI openAPI, Map<String, Schema> properties, String path) {
         if (properties == null) {
             return;
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/InlineModelResolverTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/InlineModelResolverTest.java
index caf66155197d..b9d0c5188303 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/InlineModelResolverTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/InlineModelResolverTest.java
@@ -1666,4 +1666,96 @@ public void deduplicateComponentsRewritesRefsOutsideComponentsSchemas() {
         assertRewritten("encoding headers", response.getContent().get("application/json")
                 .getEncoding().get("ok").getHeaders().get("X-Encoding").getSchema());
     }
+
+    @Test
+    public void inlineSchemaDoesNotOverwriteSpecDefinedSchemaWithMangledSameName() {
+        // The inline request body schema is registered as "importMembers_request" while the spec
+        // also defines "ImportMembersRequest". Both mangle to the same model name, so without
+        // normalization-aware collision detection one silently overwrites the other and the
+        // properties of the overwritten model disappear from the generated code.
+        OpenAPI openAPI = new OpenAPI();
+        openAPI.setComponents(new Components());
+        openAPI.setPaths(new Paths());
+
+        openAPI.getComponents().addSchemas("ImportMembersRequest", new ObjectSchema()
+                .addProperty("declaredField", new StringSchema()));
+
+        Schema inlineBody = new ObjectSchema().addProperty("inlineOnly", new StringSchema());
+        openAPI.getPaths().addPathItem("/members/import", new PathItem().post(new Operation()
+                .operationId("importMembers")
+                .requestBody(new RequestBody().content(new Content()
+                        .addMediaType("application/json", new MediaType().schema(inlineBody))))));
+
+        new InlineModelResolver().flatten(openAPI);
+
+        // the spec-defined schema must survive untouched
+        Schema declared = openAPI.getComponents().getSchemas().get("ImportMembersRequest");
+        assertNotNull(declared);
+        assertNotNull(declared.getProperties().get("declaredField"));
+        assertNull(declared.getProperties().get("inlineOnly"));
+
+        // the inline schema must be registered under a name that does not mangle onto the
+        // spec-defined one
+        assertNull(openAPI.getComponents().getSchemas().get("importMembers_request"));
+        Schema inlined = openAPI.getComponents().getSchemas().get("importMembers_request_1");
+        assertNotNull(inlined);
+        assertNotNull(inlined.getProperties().get("inlineOnly"));
+    }
+
+    @Test
+    public void inlineSchemaDoesNotOverwriteSpecDefinedSchemaNamedWithOtherSeparators() {
+        // sanitizeName turns '-', '.', ' ' and friends into '_' before the name is camelized, so
+        // `Import-Members-Request` mangles onto the same model as the inline `importMembers_request`.
+        // Normalizing on '_' alone would miss this.
+        OpenAPI openAPI = new OpenAPI();
+        openAPI.setComponents(new Components());
+        openAPI.setPaths(new Paths());
+
+        openAPI.getComponents().addSchemas("Import-Members-Request", new ObjectSchema()
+                .addProperty("declaredField", new StringSchema()));
+
+        Schema inlineBody = new ObjectSchema().addProperty("inlineOnly", new StringSchema());
+        openAPI.getPaths().addPathItem("/members/import", new PathItem().post(new Operation()
+                .operationId("importMembers")
+                .requestBody(new RequestBody().content(new Content()
+                        .addMediaType("application/json", new MediaType().schema(inlineBody))))));
+
+        new InlineModelResolver().flatten(openAPI);
+
+        Schema declared = openAPI.getComponents().getSchemas().get("Import-Members-Request");
+        assertNotNull(declared);
+        assertNotNull(declared.getProperties().get("declaredField"));
+        assertNull(declared.getProperties().get("inlineOnly"));
+
+        assertNull(openAPI.getComponents().getSchemas().get("importMembers_request"));
+        Schema inlined = openAPI.getComponents().getSchemas().get("importMembers_request_1");
+        assertNotNull(inlined);
+        assertNotNull(inlined.getProperties().get("inlineOnly"));
+    }
+
+    @Test
+    public void inlineSchemaKeepsItsNameWhenTheManglerKeepsNamesDistinct() {
+        // `Importmembersrequest` mangles to itself, not to `ImportMembersRequest`, so it is NOT a
+        // collision -- the inline schema must keep its own name rather than being pushed to _1.
+        OpenAPI openAPI = new OpenAPI();
+        openAPI.setComponents(new Components());
+        openAPI.setPaths(new Paths());
+
+        openAPI.getComponents().addSchemas("Importmembersrequest", new ObjectSchema()
+                .addProperty("declaredField", new StringSchema()));
+
+        Schema inlineBody = new ObjectSchema().addProperty("inlineOnly", new StringSchema());
+        openAPI.getPaths().addPathItem("/members/import", new PathItem().post(new Operation()
+                .operationId("importMembers")
+                .requestBody(new RequestBody().content(new Content()
+                        .addMediaType("application/json", new MediaType().schema(inlineBody))))));
+
+        new InlineModelResolver().flatten(openAPI);
+
+        assertNotNull(openAPI.getComponents().getSchemas().get("Importmembersrequest"));
+        Schema inlined = openAPI.getComponents().getSchemas().get("importMembers_request");
+        assertNotNull("no real collision, the inline schema should keep its own name", inlined);
+        assertNotNull(inlined.getProperties().get("inlineOnly"));
+        assertNull(openAPI.getComponents().getSchemas().get("importMembers_request_1"));
+    }
 }