diff --git a/src/NodaUncertaintyHelper.php b/src/NodaUncertaintyHelper.php
index 8964875..1c33a65 100644
--- a/src/NodaUncertaintyHelper.php
+++ b/src/NodaUncertaintyHelper.php
@@ -11,6 +11,11 @@ declare(strict_types = 1);
  */
 final class NodaUncertaintyHelper {
 
+    const PERSINST_INDICATORS_DISALLOWED = [
+        "Unbekannt",
+        "unbekannt",
+    ];
+
     const PERSINST_UNCERTAINTY_PREFIXES = [
         "wohl ",
         "wahrscheinlich ",
@@ -23,6 +28,12 @@ final class NodaUncertaintyHelper {
         "?",
     ];
 
+    const TIME_INDICATORS_DISALLOWED = [
+        "o.D.",
+        "Unbekannt",
+        "unbekannt",
+    ];
+
     const TIME_UNCERTAINTY_PREFIXES = [
         "um ",
         "wohl um ",
@@ -40,6 +51,11 @@ final class NodaUncertaintyHelper {
     /**
      * Substrings used to express uncertainty about the validity of a place name.
      */
+    const PLACE_INDICATORS_DISALLOWED = [
+        "Unbekannt",
+        "unbekannt",
+    ];
+
     const PLACE_UNCERTAINTY_PREFIXES = [
         "vlt. ",
         "circa ",
@@ -61,6 +77,10 @@ final class NodaUncertaintyHelper {
      */
     public static function cleanUncertaintyIndicatorsTime(string $name):string {
 
+        if (\in_array($name, self::TIME_INDICATORS_DISALLOWED, true)) {
+            return "";
+        }
+
         // Remove uncertainty prefixes
         foreach (NodaUncertaintyHelper::TIME_UNCERTAINTY_PREFIXES as $prefix) {
             if (\substr($name, 0, \strlen($prefix)) === "$prefix") {
@@ -119,6 +139,10 @@ final class NodaUncertaintyHelper {
 
         $ort_name = \trim($ort_name);
 
+        if (\in_array($ort_name, self::PLACE_INDICATORS_DISALLOWED, true)) {
+            return "";
+        }
+
         // Remove uncertainty prefixes
         foreach (NodaUncertaintyHelper::PLACE_UNCERTAINTY_PREFIXES as $prefix) {
             if (\substr($ort_name, 0, \strlen($prefix)) === "$prefix") {
@@ -177,6 +201,10 @@ final class NodaUncertaintyHelper {
 
         $value = \trim($value);
 
+        if (\in_array($value, self::PERSINST_INDICATORS_DISALLOWED, true)) {
+            return "";
+        }
+
         foreach (self::PERSINST_UNCERTAINTY_PREFIXES as $toRemove) {
             if (\mb_substr($value, 0, \mb_strlen($toRemove)) === $toRemove) {
                 $value = substr($value, \mb_strlen($toRemove));
@@ -202,7 +230,7 @@ final class NodaUncertaintyHelper {
      */
     public static function guessPersinstCertainty(string $name):bool {
 
-        $name = \strtolower($name);
+        $name = \trim(\strtolower($name));
 
         // Attempt to guess uncertainty based on prefixes.
         foreach (NodaUncertaintyHelper::PERSINST_UNCERTAINTY_PREFIXES as $prefix) {