diff --git a/CHANGES.txt b/CHANGES.txt
index 30caf4fe36..cdb2d1dc01 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -121,6 +121,7 @@ Merged from 3.0:
  * Add schema to snapshot manifest, add USING TIMESTAMP clause to ALTER TABLE statements (CASSANDRA-7190)
  * If CF has no clustering columns, any row cache is full partition cache (CASSANDRA-12499)
  * Correct log message for statistics of offheap memtable flush (CASSANDRA-12776)
+ * Explicitly set locale for string validation (CASSANDRA-12541,CASSANDRA-12542,CASSANDRA-12543,CASSANDRA-12545)
 Merged from 2.2:
  * Clean up permissions when a UDA is dropped (CASSANDRA-12720)
  * Limit colUpdateTimeDelta histogram updates to reasonable deltas (CASSANDRA-11117)
diff --git a/src/java/org/apache/cassandra/hadoop/cql3/CqlRecordWriter.java b/src/java/org/apache/cassandra/hadoop/cql3/CqlRecordWriter.java
index cdd93a98fc..d2a0d86ba0 100644
--- a/src/java/org/apache/cassandra/hadoop/cql3/CqlRecordWriter.java
+++ b/src/java/org/apache/cassandra/hadoop/cql3/CqlRecordWriter.java
@@ -125,7 +125,7 @@ class CqlRecordWriter extends RecordWriter<Map<String, ByteBuffer>, List<ByteBuf
             partitionKeyColumns = tableMetadata.getPartitionKey();
 
             String cqlQuery = CqlConfigHelper.getOutputCql(conf).trim();
-            if (cqlQuery.toLowerCase().startsWith("insert"))
+            if (cqlQuery.toLowerCase(Locale.ENGLISH).startsWith("insert"))
                 throw new UnsupportedOperationException("INSERT with CqlRecordWriter is not supported, please use UPDATE/DELETE statement");
             cql = appendKeyWhereClauses(cqlQuery);
         }
diff --git a/src/java/org/apache/cassandra/schema/SpeculativeRetryParam.java b/src/java/org/apache/cassandra/schema/SpeculativeRetryParam.java
index 58c63756e1..43447f0160 100644
--- a/src/java/org/apache/cassandra/schema/SpeculativeRetryParam.java
+++ b/src/java/org/apache/cassandra/schema/SpeculativeRetryParam.java
@@ -19,6 +19,7 @@ package org.apache.cassandra.schema;
 
 import java.text.DecimalFormat;
 import java.util.concurrent.TimeUnit;
+import java.util.Locale;
 
 import com.google.common.base.Objects;
 
@@ -88,7 +89,7 @@ public final class SpeculativeRetryParam
 
     public static SpeculativeRetryParam fromString(String value)
     {
-        if (value.toLowerCase().endsWith("ms"))
+        if (value.toLowerCase(Locale.ENGLISH).endsWith("ms"))
         {
             try
             {
@@ -100,7 +101,7 @@ public final class SpeculativeRetryParam
             }
         }
 
-        if (value.toUpperCase().endsWith(Kind.PERCENTILE.toString()))
+        if (value.toUpperCase(Locale.ENGLISH).endsWith(Kind.PERCENTILE.toString()))
         {
             double threshold;
             try
diff --git a/src/java/org/apache/cassandra/thrift/ThriftConversion.java b/src/java/org/apache/cassandra/thrift/ThriftConversion.java
index 35adddfb5f..0c5c4befe6 100644
--- a/src/java/org/apache/cassandra/thrift/ThriftConversion.java
+++ b/src/java/org/apache/cassandra/thrift/ThriftConversion.java
@@ -193,7 +193,7 @@ public class ThriftConversion
     private static boolean isSuper(String thriftColumnType)
     throws org.apache.cassandra.exceptions.InvalidRequestException
     {
-        switch (thriftColumnType.toLowerCase())
+        switch (thriftColumnType.toLowerCase(Locale.ENGLISH))
         {
             case "standard": return false;
             case "super": return true;
@@ -675,7 +675,7 @@ public class ThriftConversion
 
     private static CachingParams cachingFromTrhfit(String caching)
     {
-        switch (caching.toUpperCase())
+        switch (caching.toUpperCase(Locale.ENGLISH))
         {
             case "ALL":
                 return CachingParams.CACHE_EVERYTHING;
diff --git a/src/java/org/apache/cassandra/utils/CoalescingStrategies.java b/src/java/org/apache/cassandra/utils/CoalescingStrategies.java
index 66f8912c78..16a64df2e2 100644
--- a/src/java/org/apache/cassandra/utils/CoalescingStrategies.java
+++ b/src/java/org/apache/cassandra/utils/CoalescingStrategies.java
@@ -32,6 +32,7 @@ import java.util.List;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.LockSupport;
+import java.util.Locale;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
@@ -511,7 +512,7 @@ public class CoalescingStrategies
                                                     String displayName)
     {
         String classname = null;
-        String strategyCleaned = strategy.trim().toUpperCase();
+        String strategyCleaned = strategy.trim().toUpperCase(Locale.ENGLISH);
         switch(strategyCleaned)
         {
         case "MOVINGAVERAGE":