diff --git a/src/main/java/dk/camelot64/kickc/model/Registers.java b/src/main/java/dk/camelot64/kickc/model/Registers.java
index caf716ad3..53899e07e 100644
--- a/src/main/java/dk/camelot64/kickc/model/Registers.java
+++ b/src/main/java/dk/camelot64/kickc/model/Registers.java
@@ -3,6 +3,8 @@ package dk.camelot64.kickc.model;
 import dk.camelot64.kickc.model.values.ConstantValue;
 import dk.camelot64.kickc.model.values.Value;
 
+import java.util.Locale;
+
 /** The different registers available for a program */
 public class Registers {
 
@@ -24,7 +26,7 @@ public class Registers {
    }
 
    public static Register getRegister(String name) {
-      switch(name.toUpperCase()) {
+      switch(name.toUpperCase(Locale.ENGLISH)) {
          case "A":
             return getRegisterA();
          case "X":
diff --git a/src/main/java/dk/camelot64/kickc/model/operators/OperatorSizeOf.java b/src/main/java/dk/camelot64/kickc/model/operators/OperatorSizeOf.java
index 69f0cbd59..69ee3ff15 100644
--- a/src/main/java/dk/camelot64/kickc/model/operators/OperatorSizeOf.java
+++ b/src/main/java/dk/camelot64/kickc/model/operators/OperatorSizeOf.java
@@ -9,6 +9,8 @@ import dk.camelot64.kickc.model.values.ConstantInteger;
 import dk.camelot64.kickc.model.values.ConstantLiteral;
 import dk.camelot64.kickc.model.values.ConstantRef;
 
+import java.util.Locale;
+
 /** SizeOf operator sizeof(expr). Will be resolved into a constant as soon as the expression has been resolved enough. */
 public class OperatorSizeOf extends OperatorUnary {
 
@@ -56,7 +58,7 @@ public class OperatorSizeOf extends OperatorUnary {
       if(type instanceof SymbolTypePointer) {
          return "SIZEOF_POINTER";
       } else {
-         return "SIZEOF_" + type.getTypeName().toUpperCase().replace(" ", "_");
+         return "SIZEOF_" + type.getTypeName().toUpperCase(Locale.ENGLISH).replace(" ", "_");
       }
    }
 
diff --git a/src/main/java/dk/camelot64/kickc/model/operators/OperatorTypeId.java b/src/main/java/dk/camelot64/kickc/model/operators/OperatorTypeId.java
index c36abea37..900a562c4 100644
--- a/src/main/java/dk/camelot64/kickc/model/operators/OperatorTypeId.java
+++ b/src/main/java/dk/camelot64/kickc/model/operators/OperatorTypeId.java
@@ -8,6 +8,8 @@ import dk.camelot64.kickc.model.values.ConstantInteger;
 import dk.camelot64.kickc.model.values.ConstantLiteral;
 import dk.camelot64.kickc.model.values.ConstantRef;
 
+import java.util.Locale;
+
 /**
  * TypeId operator typeid(expr) returns byte value representing the type of the expression.
  * Will be resolved into a constant as soon as the expression has been resolved enough.
@@ -60,7 +62,7 @@ public class OperatorTypeId extends OperatorUnary {
       } else if(type instanceof SymbolTypePointer) {
          return "POINTER_" + getTypeIdConstantName(((SymbolTypePointer) type).getElementType());
       } else {
-         return type.getTypeName().toUpperCase().replace(" ", "_");
+         return type.getTypeName().toUpperCase(Locale.ENGLISH).replace(" ", "_");
       }
    }
 
diff --git a/src/main/java/dk/camelot64/kickc/passes/Pass0GenerateStatementSequence.java b/src/main/java/dk/camelot64/kickc/passes/Pass0GenerateStatementSequence.java
index 2f798dc76..e8662e9e2 100644
--- a/src/main/java/dk/camelot64/kickc/passes/Pass0GenerateStatementSequence.java
+++ b/src/main/java/dk/camelot64/kickc/passes/Pass0GenerateStatementSequence.java
@@ -135,7 +135,7 @@ public class Pass0GenerateStatementSequence extends KickCBaseVisitor<Object> {
    @Override
    public Object visitGlobalDirectiveEncoding(KickCParser.GlobalDirectiveEncodingContext ctx) {
       try {
-         this.currentEncoding = ConstantString.Encoding.valueOf(ctx.NAME().getText().toUpperCase());
+         this.currentEncoding = ConstantString.Encoding.valueOf(ctx.NAME().getText().toUpperCase(Locale.ENGLISH));
       } catch(IllegalArgumentException e) {
          throw new CompileError("Unknown string encoding " + ctx.NAME().getText(), new StatementSource(ctx));
       }
@@ -474,7 +474,7 @@ public class Pass0GenerateStatementSequence extends KickCBaseVisitor<Object> {
 
    @Override
    public AsmDirectiveClobber visitAsmDirectiveClobber(KickCParser.AsmDirectiveClobberContext ctx) {
-      String clobberString = ctx.STRING().getText().toUpperCase();
+      String clobberString = ctx.STRING().getText().toUpperCase(Locale.ENGLISH);
       clobberString = clobberString.substring(1, clobberString.length() - 1);
       if(!clobberString.matches("[AXY]*")) {
          throw new CompileError("Error! Illegal clobber value " + clobberString, new StatementSource(ctx));
@@ -761,7 +761,7 @@ public class Pass0GenerateStatementSequence extends KickCBaseVisitor<Object> {
    public Object visitDirectiveInterrupt(KickCParser.DirectiveInterruptContext ctx) {
       String interruptType;
       if(ctx.getChildCount() > 1) {
-         interruptType = ctx.getChild(2).getText().toUpperCase();
+         interruptType = ctx.getChild(2).getText().toUpperCase(Locale.ENGLISH);
       } else {
          // The default interrupt type
          interruptType = Procedure.InterruptType.DEFAULT.name();
diff --git a/src/main/java/dk/camelot64/kickc/passes/PassNStructPointerRewriting.java b/src/main/java/dk/camelot64/kickc/passes/PassNStructPointerRewriting.java
index 6fb13f681..e648a44f5 100644
--- a/src/main/java/dk/camelot64/kickc/passes/PassNStructPointerRewriting.java
+++ b/src/main/java/dk/camelot64/kickc/passes/PassNStructPointerRewriting.java
@@ -12,6 +12,7 @@ import dk.camelot64.kickc.model.types.SymbolTypePointer;
 import dk.camelot64.kickc.model.types.SymbolTypeStruct;
 import dk.camelot64.kickc.model.values.*;
 
+import java.util.Locale;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
@@ -113,7 +114,7 @@ public class PassNStructPointerRewriting extends Pass2SsaOptimization {
     * @return The name of the constant
     */
    private static String getMemberOffsetConstantName(StructDefinition structDefinition, String memberName) {
-      return "OFFSET_" + structDefinition.getType().getTypeName().toUpperCase().replace(" ", "_") + "_" + memberName.toUpperCase();
+      return "OFFSET_" + structDefinition.getType().getTypeName().toUpperCase(Locale.ENGLISH).replace(" ", "_") + "_" + memberName.toUpperCase();
    }