diff --git a/src/lsp/providers/diagnosticsProvider.ts b/src/lsp/providers/diagnosticsProvider.ts
index 42609a0f4a0506c419604a51314e932673959235..aa02c0238df9d155f0e7326555cb223035219161 100644
--- a/src/lsp/providers/diagnosticsProvider.ts
+++ b/src/lsp/providers/diagnosticsProvider.ts
@@ -279,9 +279,13 @@       let base = match.groups.helper === 'theme' ? ['theme'] : []
       let keys = match.groups.key.split(/[.\[\]]/).filter(Boolean)
       let value = dlv(state.config, [...base, ...keys])
 
-      // TODO: check that the type is valid
-      // e.g. objects are not valid
-      if (typeof value !== 'undefined') {
+      if (
+        typeof value === 'string' ||
+        typeof value === 'number' ||
+        value instanceof String ||
+        value instanceof Number ||
+        Array.isArray(value)
+      ) {
         return null
       }
 
@@ -304,7 +308,10 @@         severity:
           severity === 'error'
             ? DiagnosticSeverity.Error
             : DiagnosticSeverity.Warning,
-        message: `Unknown ${match.groups.helper} key: ${match.groups.key}`,
+        message:
+          typeof value === 'undefined'
+            ? `'${match.groups.key}' does not exist in your theme config.`
+            : `'${match.groups.key}' was found but does not resolve to a string.`,
       })
     })
   })