diff --git a/engines/glk/alan3/acode.h b/engines/glk/alan3/acode.h
index 03391b1986a..7aa1d8e92db 100644
--- a/engines/glk/alan3/acode.h
+++ b/engines/glk/alan3/acode.h
@@ -505,7 +505,7 @@ struct DictionaryEntry { /* Dictionary */
 struct ACodeHeader {
 	/* Important info */
 	char tag[4];              /* "ALAN" */
-	char version[4];          /* Version of compiler */
+	byte version[4];          /* Version of compiler */
 	Aword uid;                /* Unique id of the compiled game */
 	Aword size;               /* Size of ACD-file in Awords */
 	/* Options */
@@ -562,7 +562,7 @@ struct ACodeHeader {
 struct Pre3_0beta2Header {
 	/* Important info */
 	char tag[4];        /* "ALAN" */
-	char version[4];        /* Version of compiler */
+	byte version[4];    /* Version of compiler */
 	Aword uid;          /* Unique id of the compiled game */
 	Aword size;         /* Size of ACD-file in Awords */
 	/* Options */
@@ -618,7 +618,7 @@ struct Pre3_0beta2Header {
 struct Pre3_0alpha5Header {
 	/* Important info */
 	char tag[4];        /* "ALAN" */
-	char version[4];        /* Version of compiler */
+	byte version[4];    /* Version of compiler */
 	Aword uid;          /* Unique id of the compiled game */
 	Aword size;         /* Size of ACD-file in Awords */
 	/* Options */
diff --git a/engines/glk/alan3/compatibility.cpp b/engines/glk/alan3/compatibility.cpp
index 4668d6ea821..aedfae86ec5 100644
--- a/engines/glk/alan3/compatibility.cpp
+++ b/engines/glk/alan3/compatibility.cpp
@@ -26,42 +26,42 @@ namespace Glk {
 namespace Alan3 {
 
 /*----------------------------------------------------------------------*/
-static bool is3_0Alpha(char version[]) {
+static bool is3_0Alpha(const byte version[]) {
 	return version[3] == 3 && version[2] == 0 && version[0] == 'a';
 }
 
 /*----------------------------------------------------------------------*/
-static bool is3_0Beta(char version[]) {
+static bool is3_0Beta(const byte version[]) {
 	return version[3] == 3 && version[2] == 0 && version[0] == 'b';
 }
 
 /*----------------------------------------------------------------------*/
-static int correction(char version[]) {
+static int correction(const byte version[]) {
 	return version[1];
 }
 
 /*======================================================================*/
-bool isPreAlpha5(char version[4]) {
+bool isPreAlpha5(const byte version[4]) {
 	return is3_0Alpha(version) && correction(version) < 5;
 }
 
 /*======================================================================*/
-bool isPreBeta2(char version[4]) {
+bool isPreBeta2(const byte version[4]) {
 	return is3_0Alpha(version) || (is3_0Beta(version) && correction(version) == 1);
 }
 
 /*======================================================================*/
-bool isPreBeta3(char version[4]) {
+bool isPreBeta3(const byte version[4]) {
 	return is3_0Alpha(version) || (is3_0Beta(version) && correction(version) <= 2);
 }
 
 /*======================================================================*/
-bool isPreBeta4(char version[4]) {
+bool isPreBeta4(const byte version[4]) {
 	return is3_0Alpha(version) || (is3_0Beta(version) && correction(version) <= 3);
 }
 
 /*======================================================================*/
-bool isPreBeta5(char version[4]) {
+bool isPreBeta5(const byte version[4]) {
 	return is3_0Alpha(version) || (is3_0Beta(version) && correction(version) <= 4);
 }
 
diff --git a/engines/glk/alan3/compatibility.h b/engines/glk/alan3/compatibility.h
index 0187c72ff8b..8b759c5232d 100644
--- a/engines/glk/alan3/compatibility.h
+++ b/engines/glk/alan3/compatibility.h
@@ -29,12 +29,12 @@ namespace Glk {
 namespace Alan3 {
 
 /* FUNCTIONS: */
-extern bool isPreAlpha5(char version[4]);
-extern bool isPreBeta2(char version[4]);
-extern bool isPreBeta3(char version[4]);
-extern bool isPreBeta4(char version[4]);
-extern bool isPreBeta5(char version[4]);
-extern char *decodedGameVersion(char version[]);
+extern bool isPreAlpha5(const byte version[4]);
+extern bool isPreBeta2(const byte version[4]);
+extern bool isPreBeta3(const byte version[4]);
+extern bool isPreBeta4(const byte version[4]);
+extern bool isPreBeta5(const byte version[4]);
+extern char *decodedGameVersion(const byte version[]);
 
 } // End of namespace Alan3
 } // End of namespace Glk
diff --git a/engines/glk/alan3/main.cpp b/engines/glk/alan3/main.cpp
index 6fc5e014a63..f09a54c6bea 100644
--- a/engines/glk/alan3/main.cpp
+++ b/engines/glk/alan3/main.cpp
@@ -120,7 +120,7 @@ Common::SeekableReadStream *codfil;
   be compatible.  If header size changes this should return beta2
   header size for later versions.
 */
-static int crcStart(char version[4]) {
+static int crcStart(const byte version[4]) {
 	/* Some earlier versions had a shorter header */
 	if (isPreAlpha5(version))
 		return sizeof(Pre3_0alpha5Header) / sizeof(Aword);
@@ -229,7 +229,7 @@ static const char *decodeState(int c) {
 }
 
 /*======================================================================*/
-char *decodedGameVersion(char version[]) {
+char *decodedGameVersion(const byte version[]) {
 	static char str[100];
 	sprintf(str, "%d.%d%s%d",
 	        (int)version[3],
@@ -278,7 +278,7 @@ static void alphaRunningLaterGame(char gameState) {
 }
 
 /*----------------------------------------------------------------------*/
-static void nonDevelopmentRunningDevelopmentStateGame(char version[]) {
+static void nonDevelopmentRunningDevelopmentStateGame(const byte version[]) {
 	char errorMessage[200];
 	char versionString[100];
 
diff --git a/engines/glk/alan3/reverse.cpp b/engines/glk/alan3/reverse.cpp
index 6fa7aa56a31..4dcba1258a0 100644
--- a/engines/glk/alan3/reverse.cpp
+++ b/engines/glk/alan3/reverse.cpp
@@ -368,7 +368,7 @@ static void reverseSyntaxTablePreBeta2(Aword adr) {
 }
 
 
-static void reverseSyntaxTable(Aword adr, char version[]) {
+static void reverseSyntaxTable(Aword adr, byte version[]) {
 	if (!adr || alreadyDone(adr)) return;
 
 	if (isPreBeta2(version))
@@ -634,7 +634,7 @@ static void reverseNative() {
   */
 void reverseACD(void) {
 	ACodeHeader *hdr = (ACodeHeader *)memory;
-	char version[4];
+	byte version[4];
 	int i;
 
 	/* Make a copy of the version marking to reverse */
diff --git a/engines/glk/alan3/rules.cpp b/engines/glk/alan3/rules.cpp
index de64a8db9a2..b589168fa9b 100644
--- a/engines/glk/alan3/rules.cpp
+++ b/engines/glk/alan3/rules.cpp
@@ -243,7 +243,7 @@ void evaluateRules(RuleEntry ruleList[]) {
 
 
 /*=======================================================================*/
-void resetAndEvaluateRules(RuleEntry ruleList[], char *version) {
+void resetAndEvaluateRules(RuleEntry ruleList[], const byte *version) {
 	if (isPreBeta2(version))
 		evaluateRulesPreBeta2();
 	else if (isPreBeta3(version))
diff --git a/engines/glk/alan3/rules.h b/engines/glk/alan3/rules.h
index 849fc506aeb..65291a0a707 100644
--- a/engines/glk/alan3/rules.h
+++ b/engines/glk/alan3/rules.h
@@ -36,7 +36,7 @@ extern bool anyRuleRun;       /* Did any rule run? */
 
 /* FUNCTIONS */
 extern void initRules(Aaddr rulesTableAddress);
-extern void resetAndEvaluateRules(RuleEntry rules[], char *version);
+extern void resetAndEvaluateRules(RuleEntry rules[], const byte *version);
 extern void resetRules(void);
 extern void evaluateRules(RuleEntry rules[]);