diff --git a/src/asm/lexer.c b/src/asm/lexer.c
index e5fd594e..e26019c5 100644
--- a/src/asm/lexer.c
+++ b/src/asm/lexer.c
@@ -269,6 +269,7 @@ YY_BUFFER_STATE yy_create_buffer(FILE *f)
 	/* Convert all line endings to LF and spaces */
 
 	char *mem = pBuffer->pBuffer;
+	int32_t lineCount = 0;
 
 	while (*mem) {
 		if ((mem[0] == '\\') && (mem[1] == '\"' || mem[1] == '\\')) {
@@ -279,15 +280,22 @@ YY_BUFFER_STATE yy_create_buffer(FILE *f)
 			 || ((mem[0] == '\r') && (mem[1] == '\n'))) {
 				*mem++ = ' ';
 				*mem++ = '\n';
+				lineCount++;
 			/* LF and CR */
 			} else if ((mem[0] == '\n') || (mem[0] == '\r')) {
 				*mem++ = '\n';
+				lineCount++;
 			} else {
 				mem++;
 			}
 		}
 	}
 
+	if (mem != pBuffer->pBuffer + size) {
+		nLineNo = lineCount + 1;
+		fatalerror("Found null character");
+	}
+
 	/* Remove comments */
 
 	mem = pBuffer->pBuffer;
diff --git a/test/asm/null-in-macro.out b/test/asm/null-in-macro.out
index 13f603d2..90943ee0 100644
--- a/test/asm/null-in-macro.out
+++ b/test/asm/null-in-macro.out
@@ -1,2 +1,2 @@
-ERROR: null-in-macro.asm(1):
-    Unterminated MACRO definition.
+ERROR: null-in-macro.asm(2):
+    Found null character