diff --git a/src/libatomic_ops.mk b/src/libatomic_ops.mk
index 03db7ccf..6b36c142 100644
--- a/src/libatomic_ops.mk
+++ b/src/libatomic_ops.mk
@@ -29,7 +29,7 @@ define $(PKG)_BUILD
 
     # compile test
     '$(TARGET)-gcc' \
-        -W -Wall -Werror -pedantic \
+        -W -Wall -Werror -pedantic -std=c99 \
         '$(SOURCE_DIR)/tests/test_stack.c' -o '$(PREFIX)/$(TARGET)/bin/test-$(PKG).exe' \
         `'$(TARGET)-pkg-config' atomic_ops_gpl --cflags --libs`
 endef
diff --git a/src/libsignal-protocol-c.mk b/src/libsignal-protocol-c.mk
index 9e373065..744e49c8 100644
--- a/src/libsignal-protocol-c.mk
+++ b/src/libsignal-protocol-c.mk
@@ -16,7 +16,7 @@ define $(PKG)_BUILD
     $(MAKE) -C '$(BUILD_DIR)' -j 1 install VERBOSE=1
 
     '$(TARGET)-gcc' \
-        -W -Wall -Werror -pedantic \
+        -W -Wall -Werror -pedantic -std=c99 \
         '$(TEST_FILE)' -o '$(PREFIX)/$(TARGET)/bin/test-libsignal-protocol-c.exe' \
         `'$(TARGET)-pkg-config' libsignal-protocol-c --cflags --libs`
 endef
diff --git a/src/libssh.mk b/src/libssh.mk
index 9700fe0d..afe808c0 100644
--- a/src/libssh.mk
+++ b/src/libssh.mk
@@ -55,7 +55,7 @@ define $(PKG)_BUILD
 
     # compile test
     '$(TARGET)-gcc' \
-        -W -Wall -Werror -pedantic $($(PKG)_EXTRA_WARNINGS) \
+        -W -Wall -Werror -pedantic -std=c99 $($(PKG)_EXTRA_WARNINGS) \
         $(SOURCE_DIR)/examples/{authentication.c,knownhosts.c,connect_ssh.c,exec.c} \
         -o '$(PREFIX)/$(TARGET)/bin/test-$(PKG).exe' \
         `'$(TARGET)-pkg-config' $(PKG) --cflags --libs`