diff --git a/include/asm/warning.h b/include/asm/warning.h
index 5613799f..de854b33 100644
--- a/include/asm/warning.h
+++ b/include/asm/warning.h
@@ -21,6 +21,7 @@ enum WarningID {
 	WARNING_SHIFT,
 	WARNING_USER,
 	WARNING_SHIFT_AMOUNT,
+	WARNING_TRUNCATION,
 
 	NB_WARNINGS,
 
diff --git a/src/asm/asmy.y b/src/asm/asmy.y
index d32873bb..71aa2218 100644
--- a/src/asm/asmy.y
+++ b/src/asm/asmy.y
@@ -1190,7 +1190,7 @@ constlist_32bit_entry : /* empty */
 const_8bit	: relocconst
 		{
 			if( (!rpn_isReloc(&$1)) && (($1.nVal < -128) || ($1.nVal > 255)) )
-				yyerror("Expression must be 8-bit");
+				warning(WARNING_TRUNCATION, "Expression must be 8-bit");
 			$$ = $1;
 		}
 ;
@@ -1198,7 +1198,7 @@ const_8bit	: relocconst
 const_16bit	: relocconst
 		{
 			if ((!rpn_isReloc(&$1)) && (($1.nVal < -32768) || ($1.nVal > 65535)))
-				yyerror("Expression must be 16-bit");
+				warning(WARNING_TRUNCATION, "Expression must be 16-bit");
 			$$ = $1;
 		}
 ;
diff --git a/src/asm/warning.c b/src/asm/warning.c
index 80557158..253044a1 100644
--- a/src/asm/warning.c
+++ b/src/asm/warning.c
@@ -37,6 +37,7 @@ static enum WarningState const defaultWarnings[NB_WARNINGS] = {
 	WARNING_DISABLED, /* Shifting undefined behavior */
 	WARNING_ENABLED,  /* User warnings */
 	WARNING_DISABLED, /* Strange shift amount */
+	WARNING_ENABLED,  /* Implicit truncation loses some bits */
 };
 
 static enum WarningState warningStates[NB_WARNINGS];
@@ -72,6 +73,7 @@ static char const *warningFlags[NB_WARNINGS_ALL] = {
 	"shift",
 	"user",
 	"shift-amount",
+	"truncation",
 
 	/* Meta warnings */
 	"all",