diff --git a/src/Humanizer/Bytes/ByteSize.cs b/src/Humanizer/Bytes/ByteSize.cs
index 0edb4a5dc..42d465383 100644
--- a/src/Humanizer/Bytes/ByteSize.cs
+++ b/src/Humanizer/Bytes/ByteSize.cs
@@ -248,7 +248,9 @@ public string ToString(string format, IFormatProvider provider)
 
             format = format.Replace("#.##", "0.##");
 
-            bool has(string s) => format.IndexOf(s, StringComparison.CurrentCultureIgnoreCase) != -1;
+            var culture = provider as CultureInfo ?? CultureInfo.CurrentCulture;
+
+            bool has(string s) => culture.CompareInfo.IndexOf(format, s, CompareOptions.IgnoreCase) != -1;
             string output(double n) => n.ToString(format, provider);
 
             if (has(TerabyteSymbol))
diff --git a/src/Humanizer/Localisation/NumberToWords/AfrikaansNumberToWordsConverter.cs b/src/Humanizer/Localisation/NumberToWords/AfrikaansNumberToWordsConverter.cs
index ba56b625b..a926b24ec 100644
--- a/src/Humanizer/Localisation/NumberToWords/AfrikaansNumberToWordsConverter.cs
+++ b/src/Humanizer/Localisation/NumberToWords/AfrikaansNumberToWordsConverter.cs
@@ -149,7 +149,7 @@ private static string GetUnitValue(int number, bool isOrdinal)
         private static string RemoveOnePrefix(string toWords)
         {
             // one hundred => hundredth
-            if (toWords.IndexOf("een", StringComparison.Ordinal) == 0)
+            if (toWords.StartsWith("een", StringComparison.Ordinal))
             {
                 if (toWords.IndexOf("een en", StringComparison.Ordinal) != 0)
                 {
diff --git a/src/Humanizer/Localisation/NumberToWords/ArmenianNumberToWordsConverter.cs b/src/Humanizer/Localisation/NumberToWords/ArmenianNumberToWordsConverter.cs
index a42bb341a..9385e60d6 100644
--- a/src/Humanizer/Localisation/NumberToWords/ArmenianNumberToWordsConverter.cs
+++ b/src/Humanizer/Localisation/NumberToWords/ArmenianNumberToWordsConverter.cs
@@ -167,7 +167,7 @@ private static string GetUnitValue(long number, bool isOrdinal)
         private static string RemoveOnePrefix(string toWords)
         {
             // one hundred => hundredth
-            if (toWords.IndexOf("մեկ", StringComparison.Ordinal) == 0)
+            if (toWords.StartsWith("մեկ", StringComparison.Ordinal))
             {
                 toWords = toWords.Remove(0, 4);
             }
diff --git a/src/Humanizer/Localisation/NumberToWords/EnglishNumberToWordsConverter.cs b/src/Humanizer/Localisation/NumberToWords/EnglishNumberToWordsConverter.cs
index e2b50167c..47f01e99c 100644
--- a/src/Humanizer/Localisation/NumberToWords/EnglishNumberToWordsConverter.cs
+++ b/src/Humanizer/Localisation/NumberToWords/EnglishNumberToWordsConverter.cs
@@ -154,7 +154,7 @@ private static string GetUnitValue(long number, bool isOrdinal)
         private static string RemoveOnePrefix(string toWords)
         {
             // one hundred => hundredth
-            if (toWords.IndexOf("one", StringComparison.Ordinal) == 0)
+            if (toWords.StartsWith("one", StringComparison.Ordinal))
             {
                 toWords = toWords.Remove(0, 4);
             }
diff --git a/src/Humanizer/Localisation/NumberToWords/TamilNumberToWordsConverter.cs b/src/Humanizer/Localisation/NumberToWords/TamilNumberToWordsConverter.cs
index a79158c91..d8cc1d73d 100644
--- a/src/Humanizer/Localisation/NumberToWords/TamilNumberToWordsConverter.cs
+++ b/src/Humanizer/Localisation/NumberToWords/TamilNumberToWordsConverter.cs
@@ -269,7 +269,7 @@ private static string GetHundredsValue(ref long number)
         private static string RemoveOnePrefix(string toWords)
         {
             // one hundred => hundredth
-            if (toWords.IndexOf("one", StringComparison.Ordinal) == 0)
+            if (toWords.StartsWith("one", StringComparison.Ordinal))
                 toWords = toWords.Remove(0, 4);
 
             return toWords;