diff --git a/config/ie/options b/config/ie/options
index 986f5caedf..6904e7b3f7 100644
--- a/config/ie/options
+++ b/config/ie/options
@@ -389,7 +389,9 @@ envVarsToImport = ["PATH",
 					"CORTEX_POINTDISTRIBUTION_TILESET",
 					"OCIO",
 					"IECORE_DEBUG_WAIT",
-					"CORTEX_PERFORMANCE_TEST"]
+					"CORTEX_PERFORMANCE_TEST",
+					"IECORE_FORCE_GLOBAL_SYMBOLS",
+]
 
 ENV_VARS_TO_IMPORT= " ".join(envVarsToImport)
 
diff --git a/python/IECore/__init__.py b/python/IECore/__init__.py
index 6b7b9f65d6..b5c46bb5fe 100644
--- a/python/IECore/__init__.py
+++ b/python/IECore/__init__.py
@@ -38,22 +38,37 @@
 #
 # Some parts of the IECore library are defined purely in Python. These are shown below.
 
-# Turn on RTLD_GLOBAL to avoid the dreaded cross module RTTI
-# errors on Linux. This causes libIECore etc to be loaded into
-# the global symbol table and those symbols to be shared between
-# modules. Without it, different python modules and/or libraries
-# can end up with their own copies of symbols, which breaks a
-# great many things.
+# Set IECORE_FORCE_GLOBAL_SYMBOLS = 1 to turn on RTLD_GLOBAL to
+# avoid the dreaded cross module RTTI errors on Linux.
+#    This causes libIECore etc to be loaded into the global symbol
+#    table and those symbols to be shared between modules. Without
+#    it, different python modules and/or libraries can end up with
+#    their own copies of symbols, which breaks a great many things.
 #
 # We use the awkward "__import__" approach to avoid importing sys
 # and ctypes into the IECore namespace.
 
-if __import__( "os" ).name == 'posix':
+if __import__( "os" ).name == 'posix' and __import__( "os" ).environ.get( "IECORE_FORCE_GLOBAL_SYMBOLS" ) == "1" :
 	__import__( "sys" ).setdlopenflags(
 		__import__( "sys" ).getdlopenflags() | __import__( "ctypes" ).RTLD_GLOBAL
 	)
 
-__import__( "imath" )
+try :
+
+	# Make sure we import imath _with_ RTLD_GLOBAL. This avoids
+	# boost to_python (by-value) converter issues for imath types.
+
+	import sys
+	import ctypes
+	originalDLOpenFlags = sys.getdlopenflags()
+	sys.setdlopenflags( originalDLOpenFlags | ctypes.RTLD_GLOBAL )
+
+	__import__( "imath" )
+
+finally :
+
+	sys.setdlopenflags( originalDLOpenFlags )
+	del sys, ctypes, originalDLOpenFlags
 
 from _IECore import *
 
diff --git a/src/IECoreHoudini/plugin/Plugin.cpp b/src/IECoreHoudini/plugin/Plugin.cpp
index 10e99ab90a..98931e732c 100644
--- a/src/IECoreHoudini/plugin/Plugin.cpp
+++ b/src/IECoreHoudini/plugin/Plugin.cpp
@@ -86,7 +86,11 @@ extern "C"
 {
 	SYS_VISIBILITY_EXPORT void HoudiniDSOInit( UT_DSOInfo &dsoinfo )
 	{
-		dsoinfo.loadGlobal = true;
+		const char *forceGlobals = std::getenv( "IECORE_FORCE_GLOBAL_SYMBOLS" );
+		if( forceGlobals && !strcmp( forceGlobals, "1" ) )
+		{
+			dsoinfo.loadGlobal = true;
+		}
 	}
 }
 
diff --git a/src/IECoreMaya/plugin/Loader.cpp b/src/IECoreMaya/plugin/Loader.cpp
index 04dbd55866..922c4a601b 100644
--- a/src/IECoreMaya/plugin/Loader.cpp
+++ b/src/IECoreMaya/plugin/Loader.cpp
@@ -51,7 +51,15 @@ IECORE_EXPORT MStatus initializePlugin( MObject obj )
 
 	std::string implName = pluginPath + "/impl/" + pluginName + ".so";
 
- 	g_libraryHandle = dlopen( implName.c_str(), RTLD_NOW | RTLD_GLOBAL );
+	const char *forceGlobals = std::getenv( "IECORE_FORCE_GLOBAL_SYMBOLS" );
+	if( forceGlobals && !strcmp( forceGlobals, "1" ) )
+	{
+		g_libraryHandle = dlopen( implName.c_str(), RTLD_NOW | RTLD_GLOBAL );
+	}
+	else
+	{
+		g_libraryHandle = dlopen( implName.c_str(), RTLD_NOW );
+	}
 
 	if (! g_libraryHandle )
 	{