diff --git a/Makefile b/Makefile
index 9079eb34a..804990ce8 100644
--- a/Makefile
+++ b/Makefile
@@ -190,7 +190,6 @@ minimal :
 	PYODIDE_PACKAGES="micropip" make
 
 debug :
-	EXTRA_CFLAGS="-D DEBUG_F" \
-	EXTRA_LDFLAGS="-s ASSERTIONS=2" \
+	EXTRA_CFLAGS+="-D DEBUG_F" \
 	PYODIDE_PACKAGES+="micropip,pyparsing,pytz,packaging,kiwisolver" \
 	make
diff --git a/docs/development/building-from-sources.md b/docs/development/building-from-sources.md
index 69b383877..7cf1b8b3a 100644
--- a/docs/development/building-from-sources.md
+++ b/docs/development/building-from-sources.md
@@ -1,19 +1,23 @@
 (building_from_sources)=
 # Building from sources
 
-Building is easiest on Linux and relatively straightforward on Mac. For
-Windows, we currently recommend using the Docker image (described below) to
-build Pyodide. Another option for building on Windows is to use [WSL2](https://docs.microsoft.com/en-us/windows/wsl/install-win10) to create a Linux build environment.
+Building is easiest on Linux and relatively straightforward on Mac. For Windows,
+we currently recommend using the Docker image (described below) to build
+Pyodide. Another option for building on Windows is to use
+[WSL2](https://docs.microsoft.com/en-us/windows/wsl/install-win10) to create a
+Linux build environment.
 
 ## Build using `make`
 
-Make sure the prerequisites for [emsdk](https://github.com/emscripten-core/emsdk) are
-installed. Pyodide will build a custom, patched version of emsdk, so there is no
-need to build it yourself prior.
+Make sure the prerequisites for
+[emsdk](https://github.com/emscripten-core/emsdk) are installed. Pyodide will
+build a custom, patched version of emsdk, so there is no need to build it
+yourself prior.
 
 Additional build prerequisites are:
 
-- A working native compiler toolchain, enough to build [CPython](https://devguide.python.org/setup/#linux).
+- A working native compiler toolchain, enough to build
+  [CPython](https://devguide.python.org/setup/#linux).
 - A native Python 3.8 to run the build scripts.
 - CMake
 - PyYAML
@@ -27,7 +31,9 @@ Additional build prerequisites are:
 On Mac, you will also need:
 
 - [Homebrew](https://brew.sh/) for installing dependencies
-- System libraries in the root directory (`sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target /` should do it, see https://github.com/pyenv/pyenv/issues/1219#issuecomment-428305417)
+- System libraries in the root directory (
+  `sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target /` 
+  should do it, see https://github.com/pyenv/pyenv/issues/1219#issuecomment-428305417)
 - coreutils for md5sum and other essential Unix utilities (`brew install coreutils`)
 - cmake (`brew install cmake`)
 - Cython to compile SciPy (`brew install cython`)
@@ -35,7 +41,8 @@ On Mac, you will also need:
 - pkg-config (`brew install pkg-config`)
 - openssl (`brew install openssl`)
 - gfortran (`brew cask install gfortran`)
-- f2c: Install wget (`brew install wget`), and then run the buildf2c script from the root directory (`sudo ./tools/buildf2c`)
+- f2c: Install wget (`brew install wget`), and then run the buildf2c script from
+  the root directory (`sudo ./tools/buildf2c`)
 
 
 After installing the build prerequisites, run from the command line:
@@ -47,10 +54,10 @@ make
 ## Using Docker
 
 We provide a Debian-based Docker image on Docker Hub with the dependencies
-already installed to make it easier to build Pyodide. On top of that we provide a
-pre-built image which can be used for fast custom and partial builds of pyodide.
-Note that building from the non pre-built the Docker image is *very* slow on Mac,
-building on the host machine is preferred if at all possible.
+already installed to make it easier to build Pyodide. On top of that we provide
+a pre-built image which can be used for fast custom and partial builds of
+pyodide. Note that building from the non pre-built the Docker image is *very*
+slow on Mac, building on the host machine is preferred if at all possible.
 
 1. Install Docker
 
@@ -58,15 +65,17 @@ building on the host machine is preferred if at all possible.
 
 3. Run `make` to build.
 
-Note: You can control the resources allocated to the build by setting the env vars
-`EMSDK_NUM_CORE`, `EMCC_CORES` and `PYODIDE_JOBS` (the default for each is 4).
+Note: You can control the resources allocated to the build by setting the env
+vars `EMSDK_NUM_CORE`, `EMCC_CORES` and `PYODIDE_JOBS` (the default for each is
+4).
 
 
-If running ``make`` deterministically stops at one point in each subsequent try, increasing
-the maximum RAM usage available to the docker container might help [This is different
-from the physical RAM capacity inside the system]. Ideally, at least 3 GB of RAM
-should be available to the docker container to build Pyodide smoothly. These settings can
-be changed via Docker Preferences (See [here](https://stackoverflow.com/questions/44533319/how-to-assign-more-memory-to-docker-container)).
+If running ``make`` deterministically stops at one point in each subsequent try,
+increasing the maximum RAM usage available to the docker container might help
+[This is different from the physical RAM capacity inside the system]. Ideally,
+at least 3 GB of RAM should be available to the docker container to build
+Pyodide smoothly. These settings can be changed via Docker Preferences (See
+[here](https://stackoverflow.com/questions/44533319/how-to-assign-more-memory-to-docker-container)).
 
 You can edit the files in your source checkout on your host machine, and then
 repeatedly run `make` inside the Docker environment to test your changes.
@@ -74,27 +83,42 @@ repeatedly run `make` inside the Docker environment to test your changes.
 (partial-builds)=
 ## Partial builds
 
-To build a subset of available packages in Pyodide, set the environment
-variable `PYODIDE_PACKAGES` to a comma separated list of packages. For
-instance,
+To build a subset of available packages in Pyodide, set the environment variable
+`PYODIDE_PACKAGES` to a comma separated list of packages. For instance,
 
 ```
 PYODIDE_PACKAGES="toolz,attrs" make
 ```
 
-Dependencies of the listed packages will be built automatically as well.
-The package names must match the folder names in `packages/` exactly; in
-particular they are case sensitive.
+Dependencies of the listed packages will be built automatically as well. The
+package names must match the folder names in `packages/` exactly; in particular
+they are case sensitive.
 
 To build a minimal version of Pyodide, set `PYODIDE_PACKAGES="micropip"`. The
 packages micropip and distutils are always automatically included (but an empty
-`PYODIDE_PACKAGES` is interpreted as unset).
+`PYODIDE_PACKAGES` is interpreted as unset). As a shorthand for this, one can
+say `make minimal`.
 
 ## Environment variables
 
 Following environment variables additionally impact the build,
- - `PYODIDE_JOBS`: the `-j` option passed to the `emmake make` command when applicable for parallel compilation. Default: 3.
- - `PYODIDE_BASE_URL`: Base URL where Pyodide packages are deployed. It must
-   end with a trailing `/`. Default: `./` to load Pyodide packages from the
-   same base URL path as where `pyodide.js` is located.  Example:
+ - `PYODIDE_JOBS`: the `-j` option passed to the `emmake make` command when
+   applicable for parallel compilation. Default: 3.
+ - `PYODIDE_BASE_URL`: Base URL where Pyodide packages are deployed. It must end
+   with a trailing `/`. Default: `./` to load Pyodide packages from the same
+   base URL path as where `pyodide.js` is located.  Example:
    `https://cdn.jsdelivr.net/pyodide/dev/full/`
+ - `EXTRA_CFLAGS` : Add extra compilation flags.
+ - `EXTRA_LDFLAGS` : Add extra linker flags.
+
+Setting `EXTRA_CFLAGS="-D DEBUG_F"` provides detailed diagnostic information
+whenever error branches are taken inside of the Pyodide core code. These error
+messages are frequently helpful even when the problem is a fatal configuration
+problem and Pyodide cannot even be initialized. These error branches occur also
+in correctly working code, but they are relatively uncommon so in practice the
+amount of noise generated isn't too large. The shorthand `make debug`
+automatically sets this flag.
+
+In certain cases, setting `EXTRA_LDFLAGS="-s ASSERTIONS=1` or `ASSERTIONS=2` can
+also be helpful, but this slows down the linking and the runtime speed of
+Pyodide a lot and generates a large amount of noise in the console.
diff --git a/src/core/error_handling.c b/src/core/error_handling.c
index ff736bf22..b242577fa 100644
--- a/src/core/error_handling.c
+++ b/src/core/error_handling.c
@@ -21,7 +21,7 @@ EM_JS_NUM(errcode, log_error, (char* msg), {
 
 // Right now this is dead code (probably), please don't remove it.
 // Intended for debugging purposes.
-EM_JS_NUM(errcode, log_error_obj, (JsRef obj), {
+EM_JS_NUM(errcode, console_error_obj, (JsRef obj), {
   console.error(Module.hiwire.get_value(obj));
 });
 
@@ -114,14 +114,7 @@ wrap_exception(bool attach_python_error)
   success = true;
 finally:
   // Log an appropriate warning.
-  if (success) {
-    EM_ASM(
-      {
-        let msg = Module.hiwire.get_value($0).message;
-        console.warn("Python exception:\n" + msg + "\n");
-      },
-      jserror);
-  } else {
+  if (!success) {
     PySys_WriteStderr("Error occurred while formatting traceback:\n");
     PyErr_Print();
     if (type != NULL) {
@@ -146,11 +139,19 @@ finally:
   return jserror;
 }
 
+EM_JS_NUM(errcode, log_python_error, (JsRef jserror), {
+  let msg = Module.hiwire.get_value(jserror).message;
+  console.warn("Python exception:\n" + msg + "\n");
+  return 0;
+});
+
 void _Py_NO_RETURN
 pythonexc2js()
 {
   JsRef jserror = wrap_exception(false);
-  if (jserror == NULL) {
+  if (jserror != NULL) {
+    log_python_error(jserror);
+  } else {
     jserror =
       new_error("Error occurred while formatting traceback", Js_undefined);
   }
diff --git a/src/core/error_handling.h b/src/core/error_handling.h
index 7b02505b1..ca8ffddbe 100644
--- a/src/core/error_handling.h
+++ b/src/core/error_handling.h
@@ -22,6 +22,11 @@ extern PyObject* conversion_error;
 JsRef
 wrap_exception(bool attach_python_error);
 
+/**
+ * Argument should be output of wrap_exception.
+ */
+errcode log_python_error(JsRef);
+
 /**
  * Convert the active Python exception into a Javascript Error object and print
  * it to the console.
@@ -29,13 +34,14 @@ wrap_exception(bool attach_python_error);
 void
 pythonexc2js();
 
+// Used by LOG_EM_JS_ERROR (behind DEBUG_F flag)
 errcode
-log_error(char* msg);
+console_error(char* msg);
 
 // Right now this is dead code (probably), please don't remove it.
 // Intended for debugging purposes.
 errcode
-log_error_obj(JsRef obj);
+console_error_obj(JsRef obj);
 
 /**
  * EM_JS Wrappers
@@ -138,7 +144,7 @@ log_error_obj(JsRef obj);
              __LINE__,                                                         \
              __func__,                                                         \
              __FILE__);                                                        \
-    log_error(msg);                                                            \
+    console_error(msg);                                                        \
     free(msg);                                                                 \
     goto finally;                                                              \
   } while (0)
diff --git a/src/core/hiwire.c b/src/core/hiwire.c
index 83f53e4ee..13bc1f4c2 100644
--- a/src/core/hiwire.c
+++ b/src/core/hiwire.c
@@ -46,6 +46,11 @@ EM_JS_NUM(int, hiwire_init, (), {
   _hiwire.objects.set(Module.hiwire.TRUE, true);
   _hiwire.objects.set(Module.hiwire.FALSE, false);
 
+#ifdef DEBUG_F
+  Module.hiwire._hiwire = _hiwire;
+  let many_objects_warning_threshold = 200;
+#endif
+
   Module.hiwire.new_value = function(jsval)
   {
     // Should we guard against duplicating standard values?
@@ -60,6 +65,14 @@ EM_JS_NUM(int, hiwire_init, (), {
     let idval = _hiwire.counter[0];
     _hiwire.objects.set(idval, jsval);
     _hiwire.counter[0] += 2;
+#ifdef DEBUG_F
+    if (_hiwire.objects.size > many_objects_warning_threshold) {
+      console.warn(
+        "A fairly large number of hiwire objects are present, this could " +
+        "be a sign of a memory leak.");
+      many_objects_warning_threshold += 100;
+    }
+#endif
     return idval;
   };
 
@@ -68,13 +81,27 @@ EM_JS_NUM(int, hiwire_init, (), {
   Module.hiwire.get_value = function(idval)
   {
     if (!idval) {
+      // clang-format off
       // This might have happened because the error indicator is set. Let's
       // check.
       if (_PyErr_Occurred()) {
         // This will lead to a more helpful error message.
-        _pythonexc2js();
+        let exc = _wrap_exception();
+        let e = Module.hiwire.pop_value(exc);
+        console.error(
+          `Internal error: Argument '${idval}' to hiwire.get_value is falsy. ` +
+          "This was probably because the Python error indicator was set when get_value was called. " +
+          "The Python error that caused this was:",
+          e
+        );
+        throw e;
+      } else {
+        throw new Error(
+          `Internal error: Argument '${idval}' to hiwire.get_value is falsy`
+          + ' (but error indicator is not set).'
+        );
       }
-      throw new Error("Argument to hiwire.get_value is undefined");
+      // clang-format on
     }
     if (!_hiwire.objects.has(idval)) {
       // clang-format off