diff --git a/build.gradle.kts b/build.gradle.kts
index 5d41141..525eb43 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -24,7 +24,7 @@ plugins {
 }
 
 group = "io.github.pemistahl"
-version = "1.1.0"
+version = "1.0.2"
 
 kotlin {
     compilerOptions {
diff --git a/src/functionalTest/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogLinterPluginFunctionalTest.kt b/src/functionalTest/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogLinterPluginFunctionalTest.kt
index b915f18..f66fa11 100644
--- a/src/functionalTest/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogLinterPluginFunctionalTest.kt
+++ b/src/functionalTest/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogLinterPluginFunctionalTest.kt
@@ -101,6 +101,8 @@ class VersionCatalogLinterPluginFunctionalTest {
                 "Required order: [module | group], name (, version(.ref))",
             "Line 2: Entry with key 'activation' in section '[libraries]' must not have " +
                 "two or more adjacent whitespace characters.",
+            "Line 4: Use table notation instead of string notation for library with key 'antlr'. " +
+                "Required order: [module | group], name (, version(.ref))",
             "Line 7: Entries are not sorted alphabetically in section '[plugins]'. " +
                 "Found key 'shadowJar' where 'ktlint' was expected.",
             "Line 9: Attributes of plugin with key 'ktlint' are not sorted correctly. " +
diff --git a/src/main/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogChecker.kt b/src/main/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogChecker.kt
index 590e2f5..0de00b4 100644
--- a/src/main/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogChecker.kt
+++ b/src/main/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogChecker.kt
@@ -86,8 +86,13 @@ abstract class VersionCatalogChecker : DefaultTask() {
         for ((lineNumbers, library) in libraries) {
             val parseResult = Toml.parse(library)
             val key = parseResult.keySet().iterator().next()
+            val requiredOrder = "Required order: [module | group], name (, version(.ref))"
 
-            if (parseResult.isTable(key)) {
+            if (parseResult.isString(key)) {
+                val message =
+                    "Use table notation instead of string notation for library with key '$key'. $requiredOrder"
+                errorMessages.add(ErrorMessage(lineNumbers, message))
+            } else if (parseResult.isTable(key)) {
                 val attributes = parseResult.getTable(key)!!.keySet().iterator()
                 val firstAttribute = attributes.next()
                 val secondAttribute = attributes.next()
@@ -96,8 +101,7 @@ abstract class VersionCatalogChecker : DefaultTask() {
 
                 if (!isModuleDefined && !isGroupAndNameDefined) {
                     val message =
-                        "Attributes of library with key '$key' are not sorted correctly. " +
-                            "Required order: [module | group], name (, version(.ref))"
+                        "Attributes of library with key '$key' are not sorted correctly. $requiredOrder"
                     errorMessages.add(ErrorMessage(lineNumbers, message))
                 }
             }
diff --git a/src/test/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogCheckerTest.kt b/src/test/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogCheckerTest.kt
index a72ed4c..c9fa686 100644
--- a/src/test/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogCheckerTest.kt
+++ b/src/test/kotlin/io/github/pemistahl/versioncatalog/linter/plugin/VersionCatalogCheckerTest.kt
@@ -195,6 +195,19 @@ class VersionCatalogCheckerTest {
             ).map { it.toString() },
         )
 
+        assertEquals(
+            listOf(
+                "Line 1: Use table notation instead of string notation for library with key 'activation'. " +
+                    "Required order: [module | group], name (, version(.ref))",
+            ),
+            task.checkLibraries(
+                listOf(
+                    1..1 to "activation = \"javax.activation:com.sun.activation:1.2.0\"",
+                    2..2 to "antisamy = { module = \"org.owasp.antisamy:antisamy\", version.ref = \"antisamy\" }",
+                ),
+            ).map { it.toString() },
+        )
+
         assertEquals(
             listOf(
                 "Line 1: Attributes of library with key 'activation' are not sorted correctly. " +