diff --git a/cmd/signtool/manifest.mn b/cmd/signtool/manifest.mn
index 40be262dba..d1b9d48c0a 100644
--- a/cmd/signtool/manifest.mn
+++ b/cmd/signtool/manifest.mn
@@ -6,6 +6,10 @@ CORE_DEPTH = ../..
 
 MODULE = nss
 
+ifdef ZLIB_INCLUDE_DIR
+INCLUDES += -I$(ZLIB_INCLUDE_DIR)
+endif
+
 EXPORTS = 
 
 CSRCS = signtool.c		\
diff --git a/lib/ssl/manifest.mn b/lib/ssl/manifest.mn
index 83df8c0b87..ac37c8648c 100644
--- a/lib/ssl/manifest.mn
+++ b/lib/ssl/manifest.mn
@@ -5,6 +5,10 @@ CORE_DEPTH = ../..
 
 # DEFINES = -DTRACE
 
+ifdef ZLIB_INCLUDE_DIR
+INCLUDES += -I$(ZLIB_INCLUDE_DIR)
+endif
+
 EXPORTS = \
         ssl.h \
         sslt.h \