diff --git a/.appveyor.yml b/.appveyor.yml
index 1703ab1ec..3c91d4239 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -7,10 +7,11 @@ environment:
   GIT_LFS_SKIP_SMUDGE: 1
 
 cache:
-- sqlite-dll-win32-x86-3240000.zip -> .appveyor.yml
-- sqlite-dll-win64-x64-3240000.zip -> .appveyor.yml
-- nimbus-deps.zip -> .appveyor.yml
-- NimBinaries
+  - sqlite-dll-win32-x86-3240000.zip -> .appveyor.yml
+  - sqlite-dll-win64-x64-3240000.zip -> .appveyor.yml
+  - nimbus-deps.zip -> .appveyor.yml
+  - NimBinaries
+  - jsonTestsCache
 
 matrix:
   # We always want 32 and 64-bit compilation
@@ -60,8 +61,11 @@ install:
   - curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus/devel/build_nim.sh
   - env MAKE="mingw32-make -j2" ARCH_OVERRIDE=%PLATFORM% bash build_nim.sh Nim csources dist/nimble NimBinaries
 
+  # LFS test fixtures
+  - bash scripts\process_lfs.sh jsonTestsCache
+
 build_script:
-  - cd C:\projects\%APPVEYOR_PROJECT_SLUG%
+  #- cd C:\projects\%APPVEYOR_PROJECT_SLUG%
   - bash -c "nimble install -y --depsOnly"
 
 test_script:
diff --git a/.travis.yml b/.travis.yml
index 6dad39e2e..98b695dc1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,6 +5,7 @@ cache:
   directories:
     - NimBinaries
     - rocksdbCache
+    - jsonTestsCache
 
 git:
   # when multiple CI builds are queued, the tested commit needs to be in the last X commits cloned with "--depth X"
@@ -34,6 +35,9 @@ install:
   - curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus/devel/build_rocksdb.sh
   - bash build_rocksdb.sh rocksdbCache
 
+  # LFS test fixtures
+  - scripts/process_lfs.sh jsonTestsCache
+
 script:
   - nimble install -y --depsOnly
   - nimble test
diff --git a/Makefile b/Makefile
index 22768a3eb..8f825195d 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,8 @@ p2pd: | deps
 # Windows 10 with WSL enabled, but no distro installed, fails if "../../nimble.sh" is executed directly
 # in a Makefile recipe but works when prefixing it with `bash`. No idea how the PATH is overridden.
 test: | build deps nat-libs
-	bash ../../nimble.sh test $(NIM_PARAMS)
+	bash scripts/process_lfs.sh $(HANDLE_OUTPUT)
+	bash ../../nimble.sh test $(NIM_PARAMS) && rm -f 0000-*.json
 
 $(TOOLS): | build deps nat-libs p2pd
 	for D in $(TOOLS_DIRS); do [ -e "$${D}/$@.nim" ] && TOOL_DIR="$${D}" && break; done && \
diff --git a/beacon_chain.nimble b/beacon_chain.nimble
index 60762fbcc..539045601 100644
--- a/beacon_chain.nimble
+++ b/beacon_chain.nimble
@@ -49,7 +49,7 @@ task test, "Run all tests":
   # Minimal config
   buildBinary "all_tests", "tests/", "-r -d:release -d:chronicles_log_level=ERROR -d:const_preset=minimal"
 
-  buildBinary "test_fixture_ssz_static", "tests/official/", "-r -d:release -d:chronicles_log_level=DEBUG -d:const_preset=minimal"
+  buildBinary "test_fixture_ssz_static", "tests/official/", "-r -d:debug -d:chronicles_log_level=DEBUG -d:const_preset=minimal"
   buildBinary "test_fixture_ssz_static", "tests/official/", "-r -d:release -d:chronicles_log_level=DEBUG -d:const_preset=mainnet"
 
   # State sim; getting into 3rd epoch useful
diff --git a/scripts/process_lfs.sh b/scripts/process_lfs.sh
new file mode 100755
index 000000000..c83bef26d
--- /dev/null
+++ b/scripts/process_lfs.sh
@@ -0,0 +1,73 @@
+#!/bin/bash
+
+set -e
+
+ARCHIVE_NAME="json_tests.tar.xz"
+TMP_CACHE_DIR="tmpcache"
+SUBREPO_DIR="tests/official/fixtures"
+LFS_DIR="json_tests"
+CACHE_DIR="$1" # optional parameter pointing to a CI cache dir. Without it, we just download the LFS files for a local `make test`.
+
+[[ -d "${SUBREPO_DIR}" ]] || { echo "This script should be run from the \"nim-beacon-chain\" repo top dir."; exit 1; }
+
+# macOS quirks
+if uname | grep -qi "darwin"; then
+	ON_MACOS=1
+	STAT_FORMAT="-f %m"
+else
+	ON_MACOS=0
+	STAT_FORMAT="-c %Y"
+fi
+
+# to and from stdout
+DECOMPRESS_XZ="false"
+COMPRESS_XZ="false"
+which 7z &>/dev/null && { DECOMPRESS_XZ="7z e -txz -bd -so"; COMPRESS_XZ="7z a -txz -an -bd -si -so"; }
+which xz &>/dev/null && { DECOMPRESS_XZ="xz -d -c -T 0"; COMPRESS_XZ="xz -c -T 0"; }
+
+download_lfs_files() {
+	echo "Downloading LFS files."
+	pushd "${SUBREPO_DIR}"
+	git lfs install # redundant after running it once per repo, but fast enough not to worry about detecting whether it ran before
+	git lfs pull -I "${LFS_DIR}" # we just care about test fixtures converted from YAML to JSON
+	popd
+}
+
+UPDATE_CACHE=0
+if [[ -n "${CACHE_DIR}" ]]; then
+	if [[ -e "${CACHE_DIR}/${ARCHIVE_NAME}" ]]; then
+		# compare the archive's mtime to the date of the last commit
+		if [[ $(stat ${STAT_FORMAT} "${CACHE_DIR}/${ARCHIVE_NAME}") -gt $(cd "${SUBREPO_DIR}"; git log --pretty=format:%cd -n 1 --date=unix "${LFS_DIR}") ]]; then
+			# the cache is valid
+			echo "Copying cached files into ${SUBREPO_DIR}/${LFS_DIR}/"
+			mkdir -p "${TMP_CACHE_DIR}"
+			${DECOMPRESS_XZ} "${CACHE_DIR}/${ARCHIVE_NAME}" | tar -x -C "${TMP_CACHE_DIR}" -f -
+			cp -a "${TMP_CACHE_DIR}/${LFS_DIR}"/* "${SUBREPO_DIR}/${LFS_DIR}/"
+			rm -rf "${TMP_CACHE_DIR}"
+		else
+			# old cache
+			echo "Invalidating cache."
+			UPDATE_CACHE=1
+		fi
+	else
+		# creating the archive for the first time
+		mkdir -p "${CACHE_DIR}"
+		UPDATE_CACHE=1
+	fi
+	if [[ "${UPDATE_CACHE}" == "1" ]]; then
+		if [[ "${ON_MACOS}" == "1" ]]; then
+			brew install git-lfs # this takes almost 5 minutes on Travis, so only run it if needed
+		fi
+		download_lfs_files
+		echo "Updating the cache."
+		pushd "${SUBREPO_DIR}"
+		# the archive will contain ${LFS_DIR} as its top dir
+		git archive --format=tar HEAD "${LFS_DIR}" | ${COMPRESS_XZ} > "${ARCHIVE_NAME}"
+		popd
+		mv "${SUBREPO_DIR}/${ARCHIVE_NAME}" "${CACHE_DIR}/"
+	fi
+else
+	# no caching
+	download_lfs_files
+fi
+
diff --git a/tests/official/test_fixture_ssz_static.nim b/tests/official/test_fixture_ssz_static.nim
index 91a5798d5..2a94af0c9 100644
--- a/tests/official/test_fixture_ssz_static.nim
+++ b/tests/official/test_fixture_ssz_static.nim
@@ -74,55 +74,56 @@ proc readSszValueRef*(input: openarray[byte], T: type): ref T =
   new result
   result[] = readSszValue(input, T)
 
-proc testerImpl[T](path: string, test: SszStaticTest) {.cdecl, gcsafe.} =
-  doAssert test.obj != nil
-  var obj = SpecObject[T](test.obj)
+proc testerImpl[T](path: string, sszTest: SszStaticTest) {.cdecl, gcsafe.} =
+  doAssert sszTest.obj != nil
+  var obj = SpecObject[T](sszTest.obj)
 
-  template execTest(testOpName, testOp, expectedRes) =
-    let ourRes = testOp
-    let success = valuesAreEqual(ourRes, expectedRes)
-    if not success and traceOnFailure:
-      {.gcsafe.}:
-        echo "====== ", testOpName, " failed ", path, ":", test.line
-        echo " our result:"
-        echo "  ", ourRes
-        echo " expected result:"
-        echo "  ", expectedRes
-        when defined(serialization_tracing):
-          tracingEnabled = true
-          discard testOp
-          tracingEnabled = false
-        echo "======================================================"
-        if failFast: quit 1
+  test &"test case on line {sszTest.line}":
+    template execTest(testOpName, testOp, expectedRes) =
+      let ourRes = testOp
+      let success = valuesAreEqual(ourRes, expectedRes)
+      if not success and traceOnFailure:
+        {.gcsafe.}:
+          echo "====== ", testOpName, " failed ", path, ":", sszTest.line
+          echo " our result:"
+          echo "  ", ourRes
+          echo " expected result:"
+          echo "  ", expectedRes
+          when defined(serialization_tracing):
+            tracingEnabled = true
+            discard testOp
+            tracingEnabled = false
+          echo "======================================================"
+          if failFast: quit 1
 
-    # TODO BEWARE: Passing the boolean expression to `check` directly
-    # will trigger a Nim compilation bomb. This is most likely caused
-    # by a mis-behaving generics instantiations cache when a function
-    # is explicitly instantiated to get its address.
-    # There is a recursive instantiation loop of system's `$` operator.
-    check success
+      # TODO BEWARE: Passing the boolean expression to `check` directly
+      # will trigger a Nim compilation bomb. This is most likely caused
+      # by a mis-behaving generics instantiations cache when a function
+      # is explicitly instantiated to get its address.
+      # There is a recursive instantiation loop of system's `$` operator.
+      check success
 
-  # let ob = SSZ.encode(obj.obj)
+    # let ob = SSZ.encode(obj.obj)
 
-  when false:
-    execTest "serialization",
-              (let ourBytes = SSZ.encode(obj.obj); ourBytes),
-              test.expectedBytes
+    when false:
+      execTest "serialization",
+                (let ourBytes = SSZ.encode(obj.obj); ourBytes),
+                sszTest.expectedBytes
 
-    execTest "root hash check",
-              hashTreeRoot(obj.obj),
-              test.expectedRootHash
+      execTest "root hash check",
+                hashTreeRoot(obj.obj),
+                sszTest.expectedRootHash
 
-    when hasSigningRoot(T):
-      doAssert test.hasSigHash
-      execTest "sig hash check",
-               signingRoot(obj.obj),
-               test.expectedSigHash
+      when hasSigningRoot(T):
+        doAssert sszTest.hasSigHash
+        execTest "sig hash check",
+                 signingRoot(obj.obj),
+                 sszTest.expectedSigHash
 
-  when true:
-    execTest "roundtrip",
-           readSszValueRef(test.expectedBytes, T),
-           obj.obj
+    when true:
+      execTest "roundtrip",
+             readSszValueRef(sszTest.expectedBytes, T),
+             obj.obj
 
 template addSpecTypeRTTI(T: type) =
   var reader = readerImpl[T]
@@ -207,8 +208,7 @@ proc executeSuite(path: string) =
   let sszSuite = path.parseTests SszStaticTest
   suite &"{path}: {sszSuite.title}":
     for sszTest in sszSuite.test_cases:
-      test &"test case on line {sszTest.line}":
-        runTest path, sszTest
+      runTest path, sszTest
 
 if fileExists(minDevTestFile):
   executeSuite minDevTestFile