diff --git a/src/lib/ebus/data.cpp b/src/lib/ebus/data.cpp
index d0c0fbf9..63b740e3 100644
--- a/src/lib/ebus/data.cpp
+++ b/src/lib/ebus/data.cpp
@@ -409,7 +409,7 @@ void SingleDataField::dump(ostream& output)
 result_t SingleDataField::read(const PartType partType,
 		SymbolString& data, unsigned char offset,
 		ostringstream& output, bool leadingSeparator,
-		bool verbose, const char* fieldName, char fieldIndex,
+		bool verbose, const char* fieldName, signed char fieldIndex,
 		char separator)
 {
 	if (partType != m_partType)
@@ -1196,7 +1196,7 @@ void DataFieldSet::dump(ostream& output)
 result_t DataFieldSet::read(const PartType partType,
 		SymbolString& data, unsigned char offset,
 		ostringstream& output, bool leadingSeparator,
-		bool verbose, const char* fieldName, char fieldIndex,
+		bool verbose, const char* fieldName, signed char fieldIndex,
 		char separator)
 {
 	bool previousFullByteOffset = true, found = false, findFieldIndex = fieldName != NULL && fieldIndex >= 0;
diff --git a/src/lib/ebus/data.h b/src/lib/ebus/data.h
index a8a7a282..3f7f0037 100644
--- a/src/lib/ebus/data.h
+++ b/src/lib/ebus/data.h
@@ -217,7 +217,7 @@ public:
 	virtual result_t read(const PartType partType,
 			SymbolString& data, unsigned char offset,
 			ostringstream& output, bool leadingSeparator=false,
-			bool verbose=false, const char* fieldName=NULL, char fieldIndex=-1,
+			bool verbose=false, const char* fieldName=NULL, signed char fieldIndex=-1,
 			char separator=UI_FIELD_SEPARATOR) = 0;
 
 	/**
@@ -309,7 +309,7 @@ public:
 	virtual result_t read(const PartType partType,
 			SymbolString& data, unsigned char offset,
 			ostringstream& output, bool leadingSeparator=false,
-			bool verbose=false, const char* fieldName=NULL, char fieldIndex=-1,
+			bool verbose=false, const char* fieldName=NULL, signed char fieldIndex=-1,
 			char separator=UI_FIELD_SEPARATOR);
 
 	// @copydoc
@@ -641,7 +641,7 @@ public:
 	virtual result_t read(const PartType partType,
 			SymbolString& data, unsigned char offset,
 			ostringstream& output, bool leadingSeparator=false,
-			bool verbose=false, const char* fieldName=NULL, char fieldIndex=-1,
+			bool verbose=false, const char* fieldName=NULL, signed char fieldIndex=-1,
 			char separator=UI_FIELD_SEPARATOR);
 
 	// @copydoc
diff --git a/src/lib/ebus/message.cpp b/src/lib/ebus/message.cpp
index 29cf9742..0c6f8798 100644
--- a/src/lib/ebus/message.cpp
+++ b/src/lib/ebus/message.cpp
@@ -313,7 +313,7 @@ result_t Message::prepareSlave(SymbolString& slaveData)
 
 result_t Message::decode(const PartType partType, SymbolString& data,
 		ostringstream& output, bool leadingSeparator,
-		bool verbose, const char* fieldName, char fieldIndex,
+		bool verbose, const char* fieldName, signed char fieldIndex,
 		char separator)
 {
 	unsigned char offset;
diff --git a/src/lib/ebus/message.h b/src/lib/ebus/message.h
index 530333ed..6b992c5f 100644
--- a/src/lib/ebus/message.h
+++ b/src/lib/ebus/message.h
@@ -190,7 +190,7 @@ public:
 	 */
 	result_t decode(const PartType partType, SymbolString& data,
 			ostringstream& output, bool leadingSeparator=false,
-			bool verbose=false, const char* fieldName=NULL, char fieldIndex=-1,
+			bool verbose=false, const char* fieldName=NULL, signed char fieldIndex=-1,
 			char separator=UI_FIELD_SEPARATOR);
 
 	/**