diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/DecoderReplacementFallback.cs b/src/libraries/System.Private.CoreLib/src/System/Text/DecoderReplacementFallback.cs
index 2e4ebb3407309e105ed9e338912183a1ceaba6f7..8f769f1c45bca6f2cd1ba55e5cebec4cca2d5550 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/DecoderReplacementFallback.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/DecoderReplacementFallback.cs
@@ -25,13 +25,13 @@ public DecoderReplacementFallback(string replacement)
 
             // Make sure it doesn't have bad surrogate pairs
             bool bFoundHigh = false;
-            for (int i = 0; i < replacement.Length; i++)
+            foreach (char c in replacement)
             {
                 // Found a surrogate?
-                if (char.IsSurrogate(replacement, i))
+                if (char.IsSurrogate(c))
                 {
                     // High or Low?
-                    if (char.IsHighSurrogate(replacement, i))
+                    if (char.IsHighSurrogate(c))
                     {
                         // if already had a high one, stop
                         if (bFoundHigh)
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/EncoderReplacementFallback.cs b/src/libraries/System.Private.CoreLib/src/System/Text/EncoderReplacementFallback.cs
index 80298ca565c52a1c1726a19da177b570a4aa3160..5c93f4cc2cdb71b99a902ba8e587abc9eaf25722 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/EncoderReplacementFallback.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/EncoderReplacementFallback.cs
@@ -26,13 +26,13 @@ public EncoderReplacementFallback(string replacement)
 
             // Make sure it doesn't have bad surrogate pairs
             bool bFoundHigh = false;
-            for (int i = 0; i < replacement.Length; i++)
+            foreach (char c in replacement)
             {
                 // Found a surrogate?
-                if (char.IsSurrogate(replacement, i))
+                if (char.IsSurrogate(c))
                 {
                     // High or Low?
-                    if (char.IsHighSurrogate(replacement, i))
+                    if (char.IsHighSurrogate(c))
                     {
                         // if already had a high one, stop
                         if (bFoundHigh)