diff --git a/core/definitions.mk b/core/definitions.mk
index ec71250..8ba8eb4 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1327,7 +1327,7 @@
 define transform-classes.jar-to-emma
 $(hide) java -classpath $(EMMA_JAR) emma instr -outmode fullcopy -outfile \
     $(PRIVATE_EMMA_COVERAGE_FILE) -ip $< -d $(PRIVATE_EMMA_INTERMEDIATES_DIR) \
-    -ix $(PRIVATE_EMMA_COVERAGE_FILTER)
+    $(addprefix -ix , $(PRIVATE_EMMA_COVERAGE_FILTER))
 endef
 
 #TODO: use a smaller -Xmx value for most libraries;