diff --git a/src/MagnumPlugins/AnyShaderConverter/AnyConverter.cpp b/src/MagnumPlugins/AnyShaderConverter/AnyConverter.cpp
index 959de54ce..226612626 100644
--- a/src/MagnumPlugins/AnyShaderConverter/AnyConverter.cpp
+++ b/src/MagnumPlugins/AnyShaderConverter/AnyConverter.cpp
@@ -236,10 +236,11 @@ bool AnyConverter::doConvertFileToFile(const Stage stage, const Containers::Stri
     const Containers::StringView formatFrom = stringForFormat(
         _state->inputFormat != Format::Unspecified ? _state->inputFormat : formatForExtension("ShaderTools::AnyConverter::convertFileToFile():", from)
     );
+    if(formatFrom.isEmpty()) return {};
     const Containers::StringView formatTo = stringForFormat(
         _state->outputFormat != Format::Unspecified ? _state->outputFormat : formatForExtension("ShaderTools::AnyConverter::convertFileToFile():", to)
     );
-    if(formatFrom.isEmpty() || formatTo.isEmpty()) return {};
+    if(formatTo.isEmpty()) return {};
 
     /* Decide on a plugin name based on the format. This might result in
        invalid combinations such as SpirvToGlslShaderConverter which can't be
diff --git a/src/MagnumPlugins/AnyShaderConverter/Test/AnyConverterTest.cpp b/src/MagnumPlugins/AnyShaderConverter/Test/AnyConverterTest.cpp
index 3bea57e53..0bc8e2975 100644
--- a/src/MagnumPlugins/AnyShaderConverter/Test/AnyConverterTest.cpp
+++ b/src/MagnumPlugins/AnyShaderConverter/Test/AnyConverterTest.cpp
@@ -44,6 +44,7 @@ struct AnyConverterTest: TestSuite::Tester {
     explicit AnyConverterTest();
 
     void validate();
+    void validateUnknown();
     void validateNotSupported();
     void validatePreprocessNotSupported();
     void validatePropagateFlags();
@@ -52,6 +53,8 @@ struct AnyConverterTest: TestSuite::Tester {
     void validatePropagatePreprocess();
 
     void convert();
+    void convertUnknownInput();
+    void convertUnknownOutput();
     void convertNotSupported();
     void convertPreprocessNotSupported();
     void convertDebugInfoNotSupported();
@@ -68,8 +71,6 @@ struct AnyConverterTest: TestSuite::Tester {
     void detectConvert();
     void detectConvertExplicitFormat();
 
-    void unknown();
-
     /* Explicitly forbid system-wide plugin dependencies. Tests that need those
        have their own manager. */
     PluginManager::Manager<AbstractConverter> _manager{"nonexistent"};
@@ -100,6 +101,7 @@ constexpr struct {
 
 AnyConverterTest::AnyConverterTest() {
     addTests({&AnyConverterTest::validate,
+              &AnyConverterTest::validateUnknown,
               &AnyConverterTest::validateNotSupported,
               &AnyConverterTest::validatePreprocessNotSupported,
               &AnyConverterTest::validatePropagateFlags,
@@ -108,6 +110,8 @@ AnyConverterTest::AnyConverterTest() {
               &AnyConverterTest::validatePropagatePreprocess,
 
               &AnyConverterTest::convert,
+              &AnyConverterTest::convertUnknownInput,
+              &AnyConverterTest::convertUnknownOutput,
               &AnyConverterTest::convertNotSupported,
               &AnyConverterTest::convertPreprocessNotSupported,
               &AnyConverterTest::convertDebugInfoNotSupported,
@@ -129,8 +133,6 @@ AnyConverterTest::AnyConverterTest() {
 
     addTests({&AnyConverterTest::detectConvertExplicitFormat});
 
-    addTests({&AnyConverterTest::unknown});
-
     /* Load the plugin directly from the build tree. Otherwise it's static and
        already loaded. */
     #ifdef ANYSHADERCONVERTER_PLUGIN_FILENAME
@@ -159,6 +161,16 @@ void AnyConverterTest::validate() {
         std::make_pair(true, Utility::formatString("WARNING: {}:10: 'reserved__identifier' : identifiers containing consecutive underscores (\"__\") are reserved", filename)));
 }
 
+void AnyConverterTest::validateUnknown() {
+    Containers::Pointer<AbstractConverter> converter = _manager.instantiate("AnyShaderConverter");
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    CORRADE_COMPARE(converter->validateFile({}, "dead.cg"),
+        std::make_pair(false, ""));
+    CORRADE_COMPARE(out.str(), "ShaderTools::AnyConverter::validateFile(): cannot determine the format of dead.cg\n");
+}
+
 void AnyConverterTest::validateNotSupported() {
     CORRADE_SKIP("No plugin that would support just validation exists.");
 }
@@ -310,6 +322,24 @@ void AnyConverterTest::convert() {
         "WARNING: {}:10: 'reserved__identifier' : identifiers containing consecutive underscores (\"__\") are reserved\n", inputFilename));
 }
 
+void AnyConverterTest::convertUnknownInput() {
+    Containers::Pointer<AbstractConverter> converter = _manager.instantiate("AnyShaderConverter");
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    CORRADE_VERIFY(!converter->convertFileToFile({}, "dead.cg", "whatever.osl"));
+    CORRADE_COMPARE(out.str(), "ShaderTools::AnyConverter::convertFileToFile(): cannot determine the format of dead.cg\n");
+}
+
+void AnyConverterTest::convertUnknownOutput() {
+    Containers::Pointer<AbstractConverter> converter = _manager.instantiate("AnyShaderConverter");
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    CORRADE_VERIFY(!converter->convertFileToFile({}, "file.spv", "whatever.osl"));
+    CORRADE_COMPARE(out.str(), "ShaderTools::AnyConverter::convertFileToFile(): cannot determine the format of whatever.osl\n");
+}
+
 void AnyConverterTest::convertNotSupported() {
     CORRADE_SKIP("No plugin that would support just conversion exists.");
 }
@@ -635,16 +665,6 @@ void AnyConverterTest::detectConvertExplicitFormat() {
     #endif
 }
 
-void AnyConverterTest::unknown() {
-    std::ostringstream output;
-    Error redirectError{&output};
-
-    Containers::Pointer<AbstractConverter> converter = _manager.instantiate("AnyShaderConverter");
-    CORRADE_COMPARE(converter->validateFile({}, "dead.cg"),
-        std::make_pair(false, ""));
-    CORRADE_COMPARE(output.str(), "ShaderTools::AnyConverter::validateFile(): cannot determine the format of dead.cg\n");
-}
-
 }}}}
 
 CORRADE_TEST_MAIN(Magnum::ShaderTools::Test::AnyConverterTest)