diff --git a/src/lib-sieve/plugins/variables/ext-variables-common.c b/src/lib-sieve/plugins/variables/ext-variables-common.c
index 17083e17a..17cba7435 100644
--- a/src/lib-sieve/plugins/variables/ext-variables-common.c
+++ b/src/lib-sieve/plugins/variables/ext-variables-common.c
@@ -611,7 +611,7 @@ bool sieve_variable_assign
 
 	/* Just a precaution, caller should prevent this in the first place */
 	if ( str_len(varval) > config->max_variable_size )
-		str_truncate(varval, config->max_variable_size);
+		str_truncate_utf8(varval, config->max_variable_size);
 
 	return TRUE;
 }
@@ -632,7 +632,7 @@ bool sieve_variable_assign_cstr
 
 	/* Just a precaution, caller should prevent this in the first place */
 	if ( str_len(varval) > config->max_variable_size )
-		str_truncate(varval, config->max_variable_size);
+		str_truncate_utf8(varval, config->max_variable_size);
 
 	return TRUE;
 }
diff --git a/src/lib-sieve/plugins/variables/ext-variables-modifiers.c b/src/lib-sieve/plugins/variables/ext-variables-modifiers.c
index 578779cce..a3ffabb12 100644
--- a/src/lib-sieve/plugins/variables/ext-variables-modifiers.c
+++ b/src/lib-sieve/plugins/variables/ext-variables-modifiers.c
@@ -482,8 +482,13 @@ int sieve_variables_modifiers_apply
 	unsigned int i, modf_count;
 
 	/* Hold value within limits */
-	if ( str_len(*value) > config->max_variable_size )
-		str_truncate(*value, config->max_variable_size);
+	if ( str_len(*value) > config->max_variable_size ) {
+		/* assume variable originates from code, so copy it first */
+		string_t *new_value = t_str_new(config->max_variable_size+3);
+		str_append_str(new_value, *value);
+		*value = new_value;
+		str_truncate_utf8(*value, config->max_variable_size);
+	}
 	
 	if ( !array_is_created(modifiers) )
 		return SIEVE_EXEC_OK;
@@ -513,7 +518,7 @@ int sieve_variables_modifiers_apply
 
 			/* Hold value within limits */
 			if ( str_len(*value) > config->max_variable_size )
-				str_truncate(*value, config->max_variable_size);
+				str_truncate_utf8(*value, config->max_variable_size);
 		}
 	}
 	return SIEVE_EXEC_OK;
diff --git a/src/lib-sieve/plugins/variables/ext-variables-operands.c b/src/lib-sieve/plugins/variables/ext-variables-operands.c
index 86d4076c3..359f3bf57 100644
--- a/src/lib-sieve/plugins/variables/ext-variables-operands.c
+++ b/src/lib-sieve/plugins/variables/ext-variables-operands.c
@@ -267,7 +267,7 @@ static int opr_match_value_read
 			if ( *str_r == NULL )
 				*str_r = t_str_new(0);
 			else if ( str_len(*str_r) > config->max_variable_size )
-				str_truncate(*str_r, config->max_variable_size);
+				str_truncate_utf8(*str_r, config->max_variable_size);
 		}
 
 		return SIEVE_EXEC_OK;