diff --git a/configure.ac b/configure.ac
index 51abfdd1e..e9e07ee90 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3,6 +3,7 @@ AC_INIT(aegisub, 1.10)
 AC_CONFIG_AUX_DIR(ac)
 AM_INIT_AUTOMAKE
 AC_CONFIG_HEADER([core/posix/acconf.h])
+AC_GNU_SOURCE
 
 AC_CANONICAL_HOST
 
@@ -88,7 +89,7 @@ AC_SEARCH_LIBS([lua_call], [lua lua50],, [AC_MSG_ERROR([lua not found.])])
 AC_SEARCH_LIBS([luaopen_base], [lualib lualib50],, [AC_MSG_WARN([lualib not found, assuming lua 5.1])])
 AC_CHECK_LIB([portaudio], [Pa_Initialize],, [AC_MSG_ERROR([portaudio not found.])])
 AC_CHECK_LIB([avcodec], [avcodec_init])
-AC_CHECK_LIB([avformat], [av_frac_init])
+AC_CHECK_LIB([avformat], [av_read_frame])
 
 PKG_CHECK_MODULES([ASA], asa >= 0.3.2, [
 	CPPFLAGS="$CPPFLAGS $ASA_CFLAGS"
diff --git a/core/audio_display.cpp b/core/audio_display.cpp
index c7775ee85..115851613 100644
--- a/core/audio_display.cpp
+++ b/core/audio_display.cpp
@@ -713,6 +713,7 @@ void AudioDisplay::DrawSpectrum(wxDC &finaldc,bool weak) {
 
 		////// START OF PARALLELISED CODE //////
 		const int cpu_count = wxThread::GetCPUCount();
+		if (cpu_count < 1) cpu_count = 1;
 		std::vector<SpectrumRendererThread*> threads(cpu_count);
 		for (int i = 0; i < cpu_count; i++) {
 			// Ugh, way too many data to copy in