diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1d1baef057..8a60b54062 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -33,6 +33,18 @@ elseif("${CMAKE_C_COMPILER_ID}" MATCHES "Clang")
     -Wfloat-conversion ${CMAKE_C_FLAGS}")
 endif()
 
+# Tell Intel compiler to do arithmetic accurately.  This is needed to
+# stop the compiler from ignoring parentheses in expressions like
+# (a + b) + c and from simplifying 0.0 + x to x (which is wrong if
+# x = -0.0).
+if (CMAKE_C_COMPILER_ID STREQUAL "Intel")
+  if (MSVC)
+    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /fp:precise")
+  else ()
+    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fprotect-parens -fsigned-zeros")
+  endif ()
+endif ()
+
 #################################################################################
 # PROJ4 CMake modules
 #################################################################################
diff --git a/configure.ac b/configure.ac
index 898d8b3bab..ee5fc5073d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,6 +29,12 @@ CFLAGS="$save_CFLAGS"
 dnl We check for headers
 AC_HEADER_STDC
 
+dnl Check flag for accurate arithmetic with Intel compiler.  This is
+dnl needed to stop the compiler from ignoring parentheses in expressions
+dnl like (a + b) + c and from simplifying 0.0 + x to x (which is wrong if
+dnl x = -0.0).
+AX_CHECK_COMPILE_FLAG([-fprotect-parens -fsigned-zeros],
+        [CFLAGS="$CFLAGS -fprotect-parens -fsigned-zeros"],,[-Werror])
 dnl Check for C99 math functions
 save_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -Wall -Werror"
diff --git a/m4/ax_check_compile_flag.m4 b/m4/ax_check_compile_flag.m4
new file mode 100644
index 0000000000..dcabb92a14
--- /dev/null
+++ b/m4/ax_check_compile_flag.m4
@@ -0,0 +1,74 @@
+# ===========================================================================
+#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+#   Check whether the given FLAG works with the current language's compiler
+#   or gives an error.  (Warnings, however, are ignored)
+#
+#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+#   success/failure.
+#
+#   If EXTRA-FLAGS is defined, it is added to the current language's default
+#   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
+#   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
+#   force the compiler to issue an error when a bad flag is given.
+#
+#   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
+#
+#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
+#   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+#   Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 5
+
+AC_DEFUN([AX_CHECK_COMPILE_FLAG],
+[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
+  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
+  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
+  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+    [AS_VAR_SET(CACHEVAR,[yes])],
+    [AS_VAR_SET(CACHEVAR,[no])])
+  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
+AS_VAR_IF(CACHEVAR,yes,
+  [m4_default([$2], :)],
+  [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_COMPILE_FLAGS
diff --git a/src/geodesic.c b/src/geodesic.c
index 40dffbc1b8..91af23f9f7 100644
--- a/src/geodesic.c
+++ b/src/geodesic.c
@@ -193,12 +193,12 @@ static real AngNormalize(real x) {
   real y = fmod(x, (real)(360));
 #if defined(_MSC_VER) && _MSC_VER < 1900
   /*
-    Before version 14 (2015), Visual Studio had problems dealing
-    with -0.0.  Specifically
-      VC 10,11,12 and 32-bit compile: fmod(-0.0, 360.0) -> +0.0
-    sincosdx has a similar fix.
-    python 2.7 on Windows 32-bit machines has the same problem.
-  */
+   * Before version 14 (2015), Visual Studio had problems dealing
+   * with -0.0.  Specifically
+   *   VC 10,11,12 and 32-bit compile: fmod(-0.0, 360.0) -> +0.0
+   * sincosdx has a similar fix.
+   * python 2.7 on Windows 32-bit machines has the same problem.
+   */
   if (x == 0) y = x;
 #endif
   return y <= -180 ? y + 360 : (y <= 180 ? y : y - 360);
@@ -239,7 +239,8 @@ static void sincosdx(real x, real* sinx, real* cosx) {
   r = remquo(x, (real)(90), &q);
 #else
   r = fmod(x, (real)(360));
-  q = (int)(floor(r / 90 + (real)(0.5)));
+  /* check for NaN */
+  q = r == r ? (int)(floor(r / 90 + (real)(0.5))) : 0;
   r -= 90 * q;
 #endif
   /* now abs(r) <= 45 */
@@ -248,13 +249,13 @@ static void sincosdx(real x, real* sinx, real* cosx) {
   s = sin(r); c = cos(r);
 #if defined(_MSC_VER) && _MSC_VER < 1900
   /*
-    Before version 14 (2015), Visual Studio had problems dealing
-    with -0.0.  Specifically
-      VC 10,11,12 and 32-bit compile: fmod(-0.0, 360.0) -> +0.0
-      VC 12       and 64-bit compile:  sin(-0.0)        -> +0.0
-    AngNormalize has a similar fix.
-    python 2.7 on Windows 32-bit machines has the same problem.
-  */
+   * Before version 14 (2015), Visual Studio had problems dealing
+   * with -0.0.  Specifically
+   *   VC 10,11,12 and 32-bit compile: fmod(-0.0, 360.0) -> +0.0
+   *   VC 12       and 64-bit compile:  sin(-0.0)        -> +0.0
+   * AngNormalize has a similar fix.
+   * python 2.7 on Windows 32-bit machines has the same problem.
+   */
   if (x == 0) s = x;
 #endif
   switch ((unsigned)q & 3U) {
@@ -658,6 +659,14 @@ real geod_genposition(const struct geod_geodesicline* l,
     S12 = l->c2 * atan2(salp12, calp12) + l->A4 * (B42 - l->B41);
   }
 
+  /* In the pattern
+   *
+   *   if ((outmask & GEOD_XX) && pYY)
+   *     *pYY = YY;
+   *
+   * the second check "&& pYY" is redundant.  It's there to make the CLang
+   * static analyzer happy.
+   */
   if ((outmask & GEOD_LATITUDE) && plat2)
     *plat2 = lat2;
   if ((outmask & GEOD_LONGITUDE) && plon2)
@@ -1127,7 +1136,7 @@ real SinCosSeries(boolx sinp, real sinx, real cosx, const real c[], int n) {
   real ar, y0, y1;
   c += (n + sinp);              /* Point to one beyond last element */
   ar = 2 * (cosx - sinx) * (cosx + sinx); /* 2 * cos(2 * x) */
-  y0 = (n & 1) ? *--c : 0; y1 = 0;          /* accumulators for sum */
+  y0 = (n & 1) ? *--c : 0; y1 = 0;        /* accumulators for sum */
   /* Now n is even */
   n /= 2;
   while (n--) {
@@ -1894,7 +1903,9 @@ void geod_polygon_addedge(const struct geod_geodesic* g,
                           struct geod_polygon* p,
                           real azi, real s) {
   if (p->num) {              /* Do nothing is num is zero */
-    real lat = 0, lon = 0, S12 = 0;  /* Initialize S12 to stop Visual Studio warning */
+    /* Initialize S12 to stop Visual Studio warning.  Initialization of lat and
+     * lon is to make CLang static analyzer happy. */
+    real lat = 0, lon = 0, S12 = 0;
     geod_gendirect(g, p->lat, p->lon, azi, GEOD_LONG_UNROLL, s,
                    &lat, &lon, 0,
                    0, 0, 0, 0, p->polyline ? 0 : &S12);
@@ -2031,6 +2042,8 @@ unsigned geod_polygon_testedge(const struct geod_geodesic* g,
   tempsum = p->A[0];
   crossings = p->crossings;
   {
+    /* Initialization of lat, lon, and S12 is to make CLang static analyzer
+       happy. */
     real lat = 0, lon = 0, s12, S12 = 0;
     geod_gendirect(g, p->lat, p->lon, azi, GEOD_LONG_UNROLL, s,
                    &lat, &lon, 0,
diff --git a/src/geodesic.h b/src/geodesic.h
index cd7c2b7040..f9d612f3f9 100644
--- a/src/geodesic.h
+++ b/src/geodesic.h
@@ -132,7 +132,7 @@
  * The patch level of the geodesic library.  (This tracks the version of
  * GeographicLib.)
  **********************************************************************/
-#define GEODESIC_VERSION_PATCH 2
+#define GEODESIC_VERSION_PATCH 3
 
 /**
  * Pack the version components into a single integer.  Users should not rely on
diff --git a/src/geodtest.c b/src/geodtest.c
index 8cc481349a..1025ce08e9 100644
--- a/src/geodtest.c
+++ b/src/geodtest.c
@@ -616,7 +616,8 @@ static int GeodSolve73() {
               &lat2, &lon2, &azi2);
   result += assertEquals(lat2, 81.04623, 0.5e-5);
   result += assertEquals(lon2, -170, 0.5e-5);
-  result += assertEquals(azi2, 0, 0.5e-5);
+  result += azi2 == 0 ? 0 : 1;
+  result += 1/azi2 > 0 ? 0 : 1; /* Check that azi2 = +0.0 not -0.0 */
   return result;
 }