diff --git a/src/util/log.cpp b/src/util/log.cpp
index f89898b29..9cb3666fb 100644
--- a/src/util/log.cpp
+++ b/src/util/log.cpp
@@ -128,6 +128,7 @@ void Log::out(LogType type, const char *file, unsigned int line, const char *for
         cerr << "Failed to format log message: " << e.what() << '\n';
         o << format << '\n';
     }
+    o.flush();
     va_end(args);
 }
 
@@ -143,4 +144,5 @@ void Log::dbgPrintfMemImpl(const char *msg, const unsigned char *data, size_t si
     for(size_t i = 0; i < size; ++i)
         o << setw(2) << static_cast<int>(data[i]) << ' ';
     o << dec << nouppercase << setfill(' ') << "}:" << size << '\n';
+    o.flush();
 }
diff --git a/test/libdigidocpp_boost.cpp b/test/libdigidocpp_boost.cpp
index 5a1327fce..9b0d9674a 100644
--- a/test/libdigidocpp_boost.cpp
+++ b/test/libdigidocpp_boost.cpp
@@ -30,6 +30,9 @@
 #include <crypto/PKCS12Signer.h>
 #include <crypto/X509Crypto.h>
 #include <util/DateTime.h>
+#include <util/log.h>
+
+#include <fstream>
 
 namespace digidoc
 {
@@ -61,6 +64,35 @@ const string ASiCS::EXT = "asics";
 
 BOOST_GLOBAL_FIXTURE(TestFixture);
 
+BOOST_AUTO_TEST_SUITE(LogSuite)
+BOOST_AUTO_TEST_CASE(logEntryIsWrittenImmediately)
+{
+    const string marker = "log entry is immediately available";
+    const string path = Conf::instance()->logFile();
+    const auto size = util::File::fileSize(path);
+    INFO("%s", marker.c_str());
+
+    BOOST_CHECK_GT(util::File::fileSize(path), size);
+    ifstream log{path};
+    const string contents{istreambuf_iterator<char>{log}, istreambuf_iterator<char>{}};
+    BOOST_CHECK_NE(contents.find(marker), string::npos);
+}
+
+BOOST_AUTO_TEST_CASE(memoryLogEntryIsWrittenImmediately)
+{
+    const string marker = "memory log entry is immediately available";
+    const string path = Conf::instance()->logFile();
+    const auto size = util::File::fileSize(path);
+    const unsigned char data[] {0x01, 0x23, 0x45, 0x67};
+    DEBUGMEM(marker.c_str(), data, sizeof(data));
+
+    BOOST_CHECK_GT(util::File::fileSize(path), size);
+    ifstream log{path};
+    const string contents{istreambuf_iterator<char>{log}, istreambuf_iterator<char>{}};
+    BOOST_CHECK_NE(contents.find(marker), string::npos);
+}
+BOOST_AUTO_TEST_SUITE_END()
+
 BOOST_AUTO_TEST_SUITE(SignerSuite)
 BOOST_AUTO_TEST_CASE(signerParameters)
 {