diff --git a/.circleci/config.yml b/.circleci/config.yml
index 045171fee..1610d8d3e 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -4,7 +4,7 @@ jobs:
 
   macos-10.12.6-aat-fonts:
     macos:
-      xcode: "9.2.0"
+      xcode: "9.0.1"
     steps:
       - checkout
       - run: HOMEBREW_NO_AUTO_UPDATE=1 brew install wget autoconf automake libtool pkg-config ragel freetype glib cairo
@@ -113,7 +113,7 @@ jobs:
       - run: make -j32
       # run-shape-fuzzer-tests.py automatically runs valgrind if see available
       # but test/api runs it by request, we probably should normalize the approaches
-      - run: RUN_VALGRIND=1 make check && make -Ctest/api check-valgrind || .ci/fail.sh
+      - run: HB_TEST_SHAPE_FUZZER_TIMEOUT=3 HB_TEST_SUBSET_FUZZER_TIMEOUT=30 RUN_VALGRIND=1 make check && make -Ctest/api check-valgrind || .ci/fail.sh
       # informational for now
       - run: make -Ctest/api check-symbols || true
 
@@ -165,7 +165,7 @@ jobs:
       - run: wget https://ftp.gnome.org/pub/gnome/sources/glib/2.58/glib-2.58.1.tar.xz && tar xf glib-2.58.1.tar.xz && cd glib-2.58.1 && ./autogen.sh --with-pcre CPPFLAGS="-fsanitize=memory" LDFLAGS="-fsanitize=memory" CFLAGS="-fsanitize=memory" CXXFLAGS="-fsanitize=memory" LD=ld.lld CC=clang CXX=clang++ && make -j32 && make install && cd ..
       - run: wget http://download.savannah.gnu.org/releases/freetype/freetype-2.9.tar.bz2 && tar xf freetype-2.9.tar.bz2 && cd freetype-2.9 && ./autogen.sh && ./configure CPPFLAGS="-fsanitize=memory" LDFLAGS="-fsanitize=memory -O1 -g -fno-omit-frame-pointer" CFLAGS="-fsanitize=memory -O1 -g -fno-omit-frame-pointer" CXXFLAGS="-fsanitize=memory -O1 -g -fno-omit-frame-pointer" LD=ld.lld CC=clang CXX=clang++ && make -j32 && make install && cd ..
       - run: CPPFLAGS="-fsanitize=memory -fsanitize-memory-track-origins" LDFLAGS="-fsanitize=memory -fsanitize-memory-track-origins -O1 -g -fno-omit-frame-pointer" CFLAGS="-fsanitize=memory -fsanitize-memory-track-origins -O1 -g -fno-omit-frame-pointer" CXXFLAGS="-fsanitize=memory -fsanitize-memory-track-origins -O1 -g -fno-omit-frame-pointer" LD=ld.lld CC=clang CXX=clang++ ./autogen.sh --with-freetype --with-glib --without-icu
-      - run: make -j32 && MSAN_OPTIONS=exitcode=42 make check || .ci/fail.sh | asan_symbolize | c++filt
+      - run: make -j32 && MSAN_OPTIONS=exitcode=42 HB_TEST_SUBSET_FUZZER_TIMEOUT=12 make check || .ci/fail.sh | asan_symbolize | c++filt
 
   clang-tsan:
     docker:
@@ -181,7 +181,7 @@ jobs:
       - run: pip install fonttools
       - run: CPPFLAGS="-fsanitize=thread" LDFLAGS="-fsanitize=thread -O1 -g -fno-omit-frame-pointer" CFLAGS="-fsanitize=thread -O1 -g -fno-omit-frame-pointer" CXXFLAGS="-fsanitize=thread -O1 -g -fno-omit-frame-pointer" LD=ld.lld CC=clang CXX=clang++ ./autogen.sh --with-freetype --with-glib --with-cairo --with-icu --with-graphite2
       - run: make -j32
-      - run: make check || .ci/fail.sh | asan_symbolize | c++filt
+      - run: HB_TEST_SUBSET_FUZZER_TIMEOUT=40 make check || .ci/fail.sh | asan_symbolize | c++filt
 
   clang-ubsan:
     docker:
diff --git a/test/fuzzing/run-shape-fuzzer-tests.py b/test/fuzzing/run-shape-fuzzer-tests.py
index a2f8b5c97..94fc877d1 100755
--- a/test/fuzzing/run-shape-fuzzer-tests.py
+++ b/test/fuzzing/run-shape-fuzzer-tests.py
@@ -33,7 +33,8 @@ def cmd (command):
 		def timeout (p, is_killed):
 			is_killed['value'] = True
 			p.kill ()
-		timer = threading.Timer (2, timeout, [p, is_killed])
+		timeout_seconds = int (os.environ.get ("HB_TEST_SHAPE_FUZZER_TIMEOUT", "2"))
+		timer = threading.Timer (timeout_seconds, timeout, [p, is_killed])
 
 		try:
 			timer.start()
diff --git a/test/fuzzing/run-subset-fuzzer-tests.py b/test/fuzzing/run-subset-fuzzer-tests.py
index 297398ce3..f290e6e6e 100755
--- a/test/fuzzing/run-subset-fuzzer-tests.py
+++ b/test/fuzzing/run-subset-fuzzer-tests.py
@@ -33,7 +33,8 @@ def cmd(command):
 		def timeout(p, is_killed):
 			is_killed['value'] = True
 			p.kill()
-		timer = threading.Timer (16, timeout, [p, is_killed])
+		timeout_seconds = int (os.environ.get ("HB_TEST_SUBSET_FUZZER_TIMEOUT", "8"))
+		timer = threading.Timer (timeout_seconds, timeout, [p, is_killed])
 
 		try:
 			timer.start()