diff --git a/Makefile b/Makefile
index 3783aa641d..1e7a12d0b4 100644
--- a/Makefile
+++ b/Makefile
@@ -59,7 +59,7 @@ DIST_VERSION_FILES := ${README_PATHS} doc/daikon.texinfo doc/developer.texinfo \
 # Need to include the Dockerfiles as they are referenced from 'Requirements for
 # compiling Daikon' in the Daikon Developer manual; which is in turn referenced
 # from the 'Installation' section of the Daikon manual.
-SCRIPT_FILES := Makefile \
+SCRIPT_FILES := Makefile java-home.mak \
 	daikon.bashrc \
 	dfepl dtrace-perl dtype-perl \
 	java-cpp \
@@ -454,7 +454,7 @@ staging:
 	@echo "]2;Building Javadoc"
 	mkdir ${STAGING_DIR}/download/api
 	# Javadoc is skipped on Java 8.  Hard-coded JAVA_HOME path is a hack.
-	(export PATH=/usr/lib/jvm/java-11/bin:${PATH}; cd java; ${MAKE} SKIP_JAVADOC=0 'JAVADOC_DEST=${STAGING_DIR}/download/api' javadoc)
+	(if [ -d /usr/lib/jvm/java-11 ]; then export JAVA_HOME=/usr/lib/jvm/java-11 PATH=/usr/lib/jvm/java-11/bin:$${PATH}; fi; cd java; ${MAKE} SKIP_JAVADOC=0 'JAVADOC_DEST=${STAGING_DIR}/download/api' javadoc)
 	# Copy the documentation
 	@echo "]2;Copying documentation"
 	mkdir ${STAGING_DIR}/download/doc
diff --git a/java/Makefile b/java/Makefile
index ce436e5d69..4f152f2186 100644
--- a/java/Makefile
+++ b/java/Makefile
@@ -25,17 +25,7 @@ JAR ?= jar
 
 BuildJDKTool = BuildJDK
 
-ifeq ($(shell uname), Darwin)
-  JAVA_HOME ?= $(shell /usr/libexec/java_home)
-else
-ifeq ($(shell which javac > /dev/null 2>&1 && echo found || echo nonexistent), found)
-  JAVA_HOME ?= $(shell readlink -f $(shell which javac) | sed "s:/bin/javac::")
-else
-  $(info Failure: Here is the output of: which javac)
-  $(info $(shell which javac))
-  $(error 'which javac' had exit status 1)
-endif
-endif
+include ${DAIKONDIR}/scripts/java-home.mak
 
 # The "JAVANN" variables mean "at least version NN", except JAVA8.
 JAVA_VERSION_STRING_WITH_EA := $(shell javac -version 2>&1 | head -1 | cut "-d " -f2)
diff --git a/scripts/daikon.bashrc b/scripts/daikon.bashrc
index 9949bdde44..6ef2d27bed 100644
--- a/scripts/daikon.bashrc
+++ b/scripts/daikon.bashrc
@@ -8,10 +8,18 @@
 ##        files to .class files but have not re-made the daikon.jar file.
 ## You should not need to edit this file.
 
-if [ "$(uname)" = "Darwin" ] ; then
-  export JAVA_HOME=${JAVA_HOME:-$(/usr/libexec/java_home)}
-else
-  export JAVA_HOME=${JAVA_HOME:-$(dirname $(dirname $(readlink -f $(which javac))))}
+# This logic is the same as in java-home.mak:  use the JDK that contains the
+# javac on the PATH.  On macOS, /usr/bin/javac is a stub; then use the JDK that
+# /usr/libexec/java_home reports.
+if [ -z "$JAVA_HOME" ] ; then
+  DAIKON_JAVAC_REALPATH=$(type -P javac > /dev/null && readlink -f "$(type -P javac)")
+  if [ "$(uname)" = "Darwin" ] && [ "$DAIKON_JAVAC_REALPATH" = "/usr/bin/javac" ] ; then
+    JAVA_HOME=$(/usr/libexec/java_home)
+  elif [ -n "$DAIKON_JAVAC_REALPATH" ] ; then
+    JAVA_HOME=$(dirname "$(dirname "$DAIKON_JAVAC_REALPATH")")
+  fi
+  unset DAIKON_JAVAC_REALPATH
+  export JAVA_HOME
 fi
 if [ ! -d "$JAVA_HOME" ]; then
   echo "Cannot infer JAVA_HOME; please set it.  Aborting daikon.bashrc ."
diff --git a/scripts/java-home.mak b/scripts/java-home.mak
new file mode 100644
index 0000000000..a6aeb1af98
--- /dev/null
+++ b/scripts/java-home.mak
@@ -0,0 +1,61 @@
+# Sets JAVA_HOME, if it is not already set, to the JDK that contains the javac
+# on the PATH.  If JAVA_HOME is already set, checks that it agrees with the
+# javac on the PATH.  Requires javac to be on the PATH.
+# A JDK is recognized by its "release" file.
+# Paths that contain whitespace are not supported, because Make splits on it.
+
+JAVAC_ON_PATH := $(shell command -v javac 2>/dev/null)
+ifeq (,$(JAVAC_ON_PATH))
+  $(error javac is not on the PATH)
+endif
+ifneq (1,$(words $(JAVAC_ON_PATH)))
+  $(error The javac on the PATH, "$(JAVAC_ON_PATH)", contains whitespace, which is not supported)
+endif
+# Resolve symbolic links such as /usr/bin/javac -> /etc/alternatives/javac.
+JAVAC_ON_PATH_REALPATH := $(realpath $(JAVAC_ON_PATH))
+
+# On macOS, /usr/bin/javac is a stub that runs the javac of JAVA_HOME if it is
+# set, or else of the JDK that /usr/libexec/java_home reports.
+JAVAC_ON_PATH_IS_MACOS_STUB :=
+ifeq ($(shell uname), Darwin)
+  ifeq ($(JAVAC_ON_PATH_REALPATH), /usr/bin/javac)
+    JAVAC_ON_PATH_IS_MACOS_STUB := 1
+  endif
+endif
+
+# The JDK that contains the javac on the PATH, or empty if that javac is not
+# within a JDK (for example, it is a wrapper script or a jenv shim).
+JAVAC_ON_PATH_JDK :=
+ifndef JAVAC_ON_PATH_IS_MACOS_STUB
+  ifneq (,$(filter %/bin/javac,$(JAVAC_ON_PATH_REALPATH)))
+    ifneq (,$(wildcard $(patsubst %/bin/javac,%,$(JAVAC_ON_PATH_REALPATH))/release))
+      JAVAC_ON_PATH_JDK := $(patsubst %/bin/javac,%,$(JAVAC_ON_PATH_REALPATH))
+    endif
+  endif
+endif
+
+ifndef JAVA_HOME
+  ifdef JAVAC_ON_PATH_IS_MACOS_STUB
+    JAVA_HOME := $(shell /usr/libexec/java_home 2>/dev/null)
+    ifeq (,$(JAVA_HOME))
+      $(error /usr/libexec/java_home did not find a JDK; set JAVA_HOME or put a JDK's bin directory on the PATH)
+    endif
+  else ifdef JAVAC_ON_PATH_JDK
+    JAVA_HOME := $(JAVAC_ON_PATH_JDK)
+  else
+    $(error Cannot determine JAVA_HOME: $(JAVAC_ON_PATH) (which resolves to $(JAVAC_ON_PATH_REALPATH)) is not within a JDK; set JAVA_HOME)
+  endif
+else
+  ifneq (1,$(words $(JAVA_HOME)))
+    $(error JAVA_HOME, "$(JAVA_HOME)", contains whitespace, which is not supported)
+  endif
+  ifeq (,$(wildcard $(JAVA_HOME)/bin/javac))
+    $(error JAVA_HOME is $(JAVA_HOME), but $(JAVA_HOME)/bin/javac does not exist)
+  endif
+  # A javac that is not within a JDK is not checked.
+  ifdef JAVAC_ON_PATH_JDK
+    ifneq ($(realpath $(JAVA_HOME)/bin/javac),$(JAVAC_ON_PATH_REALPATH))
+      $(error JAVA_HOME is $(JAVA_HOME), but the javac on the PATH is $(JAVAC_ON_PATH_REALPATH); make them agree)
+    endif
+  endif
+endif
diff --git a/tests/Makefile.common b/tests/Makefile.common
index 38dde8e8cb..ba9216ad45 100644
--- a/tests/Makefile.common
+++ b/tests/Makefile.common
@@ -133,13 +133,11 @@ ifdef ESC_ON
 endif
 
 
+# MAKEFILE_COMMON_DIR is the directory containing this file, even if the user set DAIKONDIR.
+MAKEFILE_COMMON_DIR := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
+
 # DAIKONDIR is the clone of the 'daikon' project.
-# Would like to use simple '?=' but this is recursively expanded while ':=' is simply expanded.
-# The include of Makefile.user (if it exists) will change the value of MAKEFILE_LIST and thus
-# '?=' will not evaluate as we desire.
-ifeq ($(origin DAIKONDIR), undefined)
-  DAIKONDIR := $(realpath $(dir $(lastword $(MAKEFILE_LIST)))..)
-endif
+DAIKONDIR ?= $(realpath ${MAKEFILE_COMMON_DIR}/..)
 
 # COMMON_HERE is where the Makefile.common is located.
 COMMON_HERE?=${DAIKONDIR}/tests
@@ -186,21 +184,16 @@ ECLAT_SCRATCH = $(SCRATCH_FOR_DAIKON_BASE)/$(PROJECT)_eclat
 # CP_PARENTS := cp -pf --parents
 CP_PARENTS := rsync -aR
 
-ifeq ($(shell uname), Darwin)
-  JAVA_HOME ?= $(/usr/libexec/java_home)
-else
-ifeq ($(shell which javac > /dev/null 2>&1 && echo found || echo nonexistent), found)
-  JAVA_HOME ?= $(shell readlink -f $(shell which javac) | sed "s:/bin/javac::")
-else
-  $(info Failure: Here is the output of: which javac)
-  $(info $(shell which javac))
-  $(error 'which javac' had exit status 1)
-endif
-endif
+# This follows the Makefile.user includes, so that a JAVA_HOME set there takes precedence.
+include ${DAIKONDIR}/scripts/java-home.mak
 JAVA  := ${JAVA_HOME}/bin/java
-JAVAC ?= ${JAVA_HOME}/bin/javac
-
 JUNIT_CLASSPATH ?=
+ifneq (,${JUNIT_CLASSPATH})
+  # The JUnit tests require JUNIT_CLASSPATH, even if the environment sets JAVAC.
+  JAVAC := ${JAVA_HOME}/bin/javac -cp .:${JUNIT_CLASSPATH}
+else
+  JAVAC ?= ${JAVA_HOME}/bin/javac
+endif
 
 JAVALIB_CLASSPATH := ${JAVA_HOME}/jre/lib/rt.jar:${JAVA_HOME}/lib/tools.jar
 
diff --git a/tests/daikon-tests/junit/Makefile.user b/tests/daikon-tests/junit/Makefile.user
index 9c2889b925..c0917ab212 100644
--- a/tests/daikon-tests/junit/Makefile.user
+++ b/tests/daikon-tests/junit/Makefile.user
@@ -1,17 +1,4 @@
 ###########################################################################
 
-ifeq ($(shell uname), Darwin)
-  JAVA_HOME ?= $(/usr/libexec/java_home)
-else
-ifeq ($(shell which javac > /dev/null 2>&1 && echo found || echo nonexistent), found)
-  JAVA_HOME ?= $(shell readlink -f $(shell which javac) | sed "s:/bin/javac::")
-else
-  $(info Failure: Here is the output of: which javac)
-  $(info $(shell which javac))
-  $(error 'which javac' had exit status 1)
-endif
-endif
-
 # need junit.jar on classpath to compile all junit references
 JUNIT_CLASSPATH := ${DAIKONDIR}/java/lib/*
-JAVAC := $(JAVA_HOME)/bin/javac -cp .:$(JUNIT_CLASSPATH)
diff --git a/tests/daikon-tests/junit5/Makefile.user b/tests/daikon-tests/junit5/Makefile.user
index d10d1f57d7..8a61e160f6 100644
--- a/tests/daikon-tests/junit5/Makefile.user
+++ b/tests/daikon-tests/junit5/Makefile.user
@@ -1,18 +1,5 @@
 ###########################################################################
 
-ifeq ($(shell uname), Darwin)
-  JAVA_HOME ?= $(/usr/libexec/java_home)
-else
-ifeq ($(shell which javac > /dev/null 2>&1 && echo found || echo nonexistent), found)
-  JAVA_HOME ?= $(shell readlink -f $(shell which javac) | sed "s:/bin/javac::")
-else
-  $(info Failure: Here is the output of: which javac)
-  $(info $(shell which javac))
-  $(error 'which javac' had exit status 1)
-endif
-endif
-
 # need junit.jar on classpath to compile all junit references
 # explicit order is necessary to get versions built with JDK 8 not 5
 JUNIT_CLASSPATH := ${DAIKONDIR}/java/lib/junit-4.13.2-Daikon.jar:${DAIKONDIR}/java/lib/hamcrest-core-1.3-Daikon.jar:${DAIKONDIR}/java/lib/*
-JAVAC := $(JAVA_HOME)/bin/javac -cp .:$(JUNIT_CLASSPATH)