Failed WebGL target when building in Linux environment

I'm building a WebGL target in the new Linux Editor (5.4.0b13+20160406). The build is failing with the error System.NotSupportedException: Don't know how to get python path on current platform!. The exact same project builds fine when using the editor in my OSX environment. I need it to work in the Linux environment as that's running our CI server.

There doesn't appear to be anything different with the Python environment between my mac and the linux CI server. Here's a snippet of the error:

 Unhandled Exception:
 System.NotSupportedException: Don't know how to get python path on current platform!
   at Unity.IL2CPP.Building.ToolChains.EmscriptenPaths.get_Python () [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.ToolChains.EmscriptenToolChain.CompilerExecutableFor (NiceIO.NPath sourceFile) [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.CppProgramBuilder.ProvideObjectFile (Unity.IL2CPP.Building.CppCompilationInstruction cppCompilationInstruction) [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.ParallelFor+<RunWithResult>c__AnonStorey1`2[Unity.IL2CPP.Building.CppCompilationInstruction,Unity.IL2CPP.Building.ProvideObjectResult].<>m__0 (System.Object o) [0x00000] in <filename unknown>:0 
   at System.Threading.Thread.StartInternal () [0x00000] in <filename unknown>:0 
 [ERROR] FATAL UNHANDLED EXCEPTION: System.NotSupportedException: Don't know how to get python path on current platform!
   at Unity.IL2CPP.Building.ToolChains.EmscriptenPaths.get_Python () [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.ToolChains.EmscriptenToolChain.CompilerExecutableFor (NiceIO.NPath sourceFile) [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.CppProgramBuilder.ProvideObjectFile (Unity.IL2CPP.Building.CppCompilationInstruction cppCompilationInstruction) [0x00000] in <filename unknown>:0 
   at Unity.IL2CPP.Building.ParallelFor+<RunWithResult>c__AnonStorey1`2[Unity.IL2CPP.Building.CppCompilationInstruction,Unity.IL2CPP.Building.ProvideObjectResult].<>m__0 (System.Object o) [0x00000] in <filename unknown>:0 
   at System.Threading.Thread.StartInternal () [0x00000] in <filename unknown>:0 
 
 UnityEngine.DebugLogHandler:Internal_Log(LogType, String, Object)
 UnityEngine.DebugLogHandler:LogFormat(LogType, Object, String, Object[])
 UnityEngine.Logger:Log(LogType, Object)
 UnityEngine.Debug:LogError(Object)
 UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase, Action`1) (at /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:98)
 UnityEditorInternal.IL2CPPBuilder:ConvertPlayerDlltoCpp(ICollection`1, String, String) (at /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:350)
 UnityEditorInternal.IL2CPPBuilder:Run() (at /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:213)
 UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry, Boolean) (at /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:139)
 UnityEditor.WebGL.WebGlBuildPostprocessor:PostProcess(BuildPostProcessArgs) (at /Users/builduser/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:392)
 UnityEditor.PostprocessBuildPlayer:Postprocess(BuildTarget, String, String, String, Int32, Int32, String, String, BuildOptions, RuntimeClassRegistry, BuildReport) (at /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:177)
 UnityEditor.BuildPipeline:BuildPlayerInternalNoCheck(String[], String, BuildTarget, BuildOptions, Boolean)
 UnityEditor.BuildPipeline:BuildPlayerInternal(String[], String, BuildTarget, BuildOptions) (at /home/builduser/buildslave/unity/build/artifacts/generated/common/editor/BuildPipelineBindings.gen.cs:247)
 UnityEditor.BuildPipeline:BuildPlayer(String[], String, BuildTarget, BuildOptions) (at /home/builduser/buildslave/unity/build/artifacts/generated/common/editor/BuildPipelineBindings.gen.cs:182)
 BuildScript:BuildAlphaWeb() (at Assets/Editor/BuildScript.cs:37)
  
 (Filename: /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs Line: 98)
 
 Exception: /opt/Unity/Editor/Data/il2cpp/build/il2cpp.exe did not run properly!
   at UnityEditorInternal.Runner.RunManagedProgram (System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser, System.Action`1 setupStartInfo) [0x00160] in /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:100 
   at UnityEditorInternal.IL2CPPBuilder.ConvertPlayerDlltoCpp (ICollection`1 userAssemblies, System.String outputDirectory, System.String workingDirectory) [0x002b0] in /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:350 
   at UnityEditorInternal.IL2CPPBuilder.Run () [0x0008b] in /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:213 
   at UnityEditorInternal.IL2CPPUtils.RunIl2Cpp (System.String stagingAreaData, IIl2CppPlatformProvider platformProvider, System.Action`1 modifyOutputBeforeCompile, UnityEditor.RuntimeClassRegistry runtimeClassRegistry, Boolean developmentBuild) [0x0000d] in /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:139 
   at UnityEditor.WebGL.WebGlBuildPostprocessor.PostProcess (BuildPostProcessArgs args) [0x001ee] in /Users/builduser/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:392 
   at UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) [0x000ce] in /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:177 
 UnityEditor.BuildPipeline:BuildPlayerInternalNoCheck(String[], String, BuildTarget, BuildOptions, Boolean)
 UnityEditor.BuildPipeline:BuildPlayerInternal(String[], String, BuildTarget, BuildOptions) (at /home/builduser/buildslave/unity/build/artifacts/generated/common/editor/BuildPipelineBindings.gen.cs:247)
 UnityEditor.BuildPipeline:BuildPlayer(String[], String, BuildTarget, BuildOptions) (at /home/builduser/buildslave/unity/build/artifacts/generated/common/editor/BuildPipelineBindings.gen.cs:182)
 BuildScript:BuildAlphaWeb() (at Assets/Editor/BuildScript.cs:37)
  
 (Filename: /home/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs Line: 100)
 
 DisplayProgressNotification: Build Failed
 Error building Player: 2 errors