diff --git a/contrib/Dockerfile.builder b/contrib/Dockerfile.builder
index 4f00d440f..b6918b546 100644
--- a/contrib/Dockerfile.builder
+++ b/contrib/Dockerfile.builder
@@ -3,6 +3,7 @@ MAINTAINER Christian Decker <decker.christian@gmail.com>
 
 ENV DEBIAN_FRONTEND noninteractive
 ENV BITCOIN_VERSION 0.16.0
+
 WORKDIR /build
 
 RUN apt-get -qq update && \
@@ -16,6 +17,7 @@ RUN apt-get -qq update && \
 	software-properties-common \
 	build-essential \
 	autoconf \
+	locales \
 	libtool \
 	libprotobuf-c-dev \
 	libsqlite3-dev \
@@ -33,6 +35,11 @@ RUN apt-get -qq update && \
 	wget && \
 	rm -rf /var/lib/apt/lists/*
 
+ENV LANGUAGE=en_US.UTF-8
+ENV LANG=en_US.UTF-8
+ENV LC_ALL=en_US.UTF-8
+RUN locale-gen en_US.UTF-8 && dpkg-reconfigure locales
+
 RUN cd /tmp/ && \
     wget https://bitcoin.org/bin/bitcoin-core-$BITCOIN_VERSION/bitcoin-$BITCOIN_VERSION-x86_64-linux-gnu.tar.gz -O bitcoin.tar.gz && \
     tar -xvzf bitcoin.tar.gz && \
@@ -40,4 +47,4 @@ RUN cd /tmp/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-$BITCOIN_VERSION
 
 RUN pip3 install --upgrade pip && \
-    pip3 install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1
+    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1
diff --git a/contrib/Dockerfile.builder.i386 b/contrib/Dockerfile.builder.i386
index 1684c9de3..fe0f50871 100644
--- a/contrib/Dockerfile.builder.i386
+++ b/contrib/Dockerfile.builder.i386
@@ -3,6 +3,7 @@ MAINTAINER Christian Decker <decker.christian@gmail.com>
 
 ENV DEBIAN_FRONTEND noninteractive
 ENV BITCOIN_VERSION 0.16.0
+
 WORKDIR /build
 
 RUN apt-get -qq update && \
@@ -16,6 +17,7 @@ RUN apt-get -qq update && \
 	software-properties-common \
 	build-essential \
 	autoconf \
+	locales \
 	libtool \
 	libprotobuf-c-dev \
 	libsqlite3-dev \
@@ -33,6 +35,11 @@ RUN apt-get -qq update && \
 	wget && \
 	rm -rf /var/lib/apt/lists/*
 
+ENV LANGUAGE=en_US.UTF-8
+ENV LANG=en_US.UTF-8
+ENV LC_ALL=en_US.UTF-8
+RUN locale-gen en_US.UTF-8 && dpkg-reconfigure locales
+
 RUN cd /tmp/ && \
     wget https://bitcoin.org/bin/bitcoin-core-$BITCOIN_VERSION/bitcoin-$BITCOIN_VERSION-i686-pc-linux-gnu.tar.gz -O bitcoin.tar.gz && \
     tar -xvzf bitcoin.tar.gz && \
@@ -40,4 +47,4 @@ RUN cd /tmp/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-$BITCOIN_VERSION
 
 RUN pip3 install --upgrade pip && \
-    pip3 install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1
+    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1