diff --git a/lib/importproject.cpp b/lib/importproject.cpp
index 0e6ca353480..242c1719ba9 100644
--- a/lib/importproject.cpp
+++ b/lib/importproject.cpp
@@ -1653,7 +1653,18 @@ bool ImportProject::importCppcheckGuiProject(std::istream &istr, Settings &setti
 
     for (const std::string &p : paths)
         guiProject.pathNames.push_back(Path::fromNativeSeparators(p));
-    supprs.nomsg.addSuppressions(std::move(suppressions)); // TODO: check result
+
+    bool ok = true;
+    for (const auto &suppression : suppressions) {
+        const std::string addError = supprs.nomsg.addSuppression(suppression);
+        if (!addError.empty()) {
+            errors.emplace_back(addError);
+            ok = false;
+        }
+    }
+    if (!ok)
+        return false;
+
     settings.checkHeaders = temp.checkHeaders;
     settings.checkUnusedTemplates = temp.checkUnusedTemplates;
     settings.maxCtuDepth = temp.maxCtuDepth;
diff --git a/test/cli/more-projects_test.py b/test/cli/more-projects_test.py
index 504a2b14431..98304bbe8aa 100644
--- a/test/cli/more-projects_test.py
+++ b/test/cli/more-projects_test.py
@@ -173,7 +173,6 @@ def test_project_empty_fields(tmpdir):
   </libraries>
   <suppressions/>
   <suppressions>
-    <suppression/>
   </suppressions>
   <vs-configurations/>
   <vs-configurations>
diff --git a/test/cli/project-suppressions.py b/test/cli/project-suppressions.py
new file mode 100644
index 00000000000..e2b6ba5e7d6
--- /dev/null
+++ b/test/cli/project-suppressions.py
@@ -0,0 +1,33 @@
+
+# python -m pytest project-suppressions.py
+
+from testutils import create_gui_project_file, assert_cppcheck
+
+def test_cli_and_project_suppressions(tmp_path):
+    # Uninitvar suppressed in project file
+    suppressions = [{ 'id': 'uninitvar' }]
+    project_path = tmp_path / 'project.cppcheck'
+    create_gui_project_file(project_path, root_path=str(tmp_path), suppressions=suppressions)
+
+    # Uninitvar suppressed on command line before import
+    args = ['--suppress=uninitvar', f'--project={project_path}']
+    out_exp = [
+        "cppcheck: error: suppression 'uninitvar' already exists",
+        f"cppcheck: error: failed to load project '{project_path}'. An error occurred."
+    ]
+    assert_cppcheck(args, ec_exp=1, out_exp=out_exp)
+
+def test_multiple_cli_and_project_suppressions(tmp_path):
+    # Uninitvar and unreadVariable suppressed in project file
+    suppressions = [{ 'id': 'uninitvar' }, { 'id': 'unreadVariable' },]
+    project_path = tmp_path / 'project.cppcheck'
+    create_gui_project_file(project_path, root_path=str(tmp_path), suppressions=suppressions)
+
+    # Uninitvar and unreadVariable suppressed on command line before import
+    args = ['--suppress=uninitvar', '--suppress=unreadVariable', f'--project={project_path}']
+    out_exp = [
+        "cppcheck: error: suppression 'uninitvar' already exists",
+        "cppcheck: error: suppression 'unreadVariable' already exists",
+        f"cppcheck: error: failed to load project '{project_path}'. An error occurred."
+    ]
+    assert_cppcheck(args, ec_exp=1, out_exp=out_exp)
diff --git a/test/testimportproject.cpp b/test/testimportproject.cpp
index c9889445c3c..873272030f6 100644
--- a/test/testimportproject.cpp
+++ b/test/testimportproject.cpp
@@ -79,6 +79,7 @@ class TestImportProject : public TestFixture {
         TEST_CASE(importCompileCommandsDirectoryMissing); // 'directory' field missing
         TEST_CASE(importCompileCommandsDirectoryInvalid); // 'directory' field not a string
         TEST_CASE(importCppcheckGuiProject);
+        TEST_CASE(importCppcheckGuiProjectDuplicateSuppressions);
         TEST_CASE(importCppcheckGuiProjectPremiumMisra);
         TEST_CASE(ignorePaths);
         TEST_CASE(testVcxprojUnicode);
@@ -536,6 +537,26 @@ class TestImportProject : public TestFixture {
         ASSERT_EQUALS(true, s.inlineSuppressions);
     }
 
+    void importCppcheckGuiProjectDuplicateSuppressions() const {
+        REDIRECT;
+        constexpr char xml[] = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+                               "<project version=\"1\">\n"
+                               "    <root name=\".\"/>\n"
+                               "    <project-name>test test</project-name>\n"
+                               "    <suppressions>\n"
+                               "        <suppression>uninitvar</suppression>\n"
+                               "        <suppression>uninitvar</suppression>\n"
+                               "    </suppressions>\n"
+                               "</project>\n";
+        std::istringstream istr(xml);
+        Settings s;
+        Suppressions supprs;
+        TestImporter project;
+        ASSERT_EQUALS(false, project.importCppcheckGuiProject(istr, s, supprs));
+        ASSERT_EQUALS(1, project.errors.size());
+        ASSERT_EQUALS("suppression 'uninitvar' already exists", project.errors[0]);
+    }
+
     void importCppcheckGuiProjectPremiumMisra() const {
         REDIRECT;
         constexpr char xml[] = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"