diff --git a/CMakeLists.txt b/CMakeLists.txt
index f968b3b3d..604c9b47a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -330,7 +330,7 @@ set(GNSSSDR_GNSS_SIM_LOCAL_VERSION "master")
 set(GNSSSDR_GPSTK_LOCAL_VERSION "8.0.0")
 set(GNSSSDR_MATIO_LOCAL_VERSION "1.5.19")
 set(GNSSSDR_PUGIXML_LOCAL_VERSION "1.11.4")
-set(GNSSSDR_PROTOCOLBUFFERS_LOCAL_VERSION "3.15.2")
+set(GNSSSDR_PROTOCOLBUFFERS_LOCAL_VERSION "3.15.5")
 set(GNSSSDR_BENCHMARK_LOCAL_VERSION "1.5.2")
 set(GNSSSDR_MATHJAX_EXTERNAL_VERSION "2.7.7")
 
diff --git a/README.md b/README.md
index 220912c66..d0402a3c9 100644
--- a/README.md
+++ b/README.md
@@ -395,9 +395,9 @@ $ sudo apt-get install autoconf automake libtool curl make g++ unzip
 and then:
 
 ```
-$ wget https://github.com/protocolbuffers/protobuf/releases/download/v3.13.0/protobuf-cpp-3.13.0.tar.gz
-$ tar xvfz protobuf-cpp-3.13.0.tar.gz
-$ cd protobuf-3.13.0
+$ wget https://github.com/protocolbuffers/protobuf/releases/download/v3.15.5/protobuf-cpp-3.15.5.tar.gz
+$ tar xvfz protobuf-cpp-3.15.5.tar.gz
+$ cd protobuf-3.15.5
 $ ./autogen.sh
 $ ./configure
 $ make