diff --git a/auxiliary/hat-test.c b/auxiliary/hat-test.c
index e41a53a..4f8dc65 100644
--- a/auxiliary/hat-test.c
+++ b/auxiliary/hat-test.c
@@ -5,7 +5,7 @@
  */
 
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/auxiliary/hatgen.c b/auxiliary/hatgen.c
index d9c6d73..9574cb8 100644
--- a/auxiliary/hatgen.c
+++ b/auxiliary/hatgen.c
@@ -16,7 +16,7 @@
  */
 
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/blackbox.c b/blackbox.c
index 69959b6..69ec12c 100644
--- a/blackbox.c
+++ b/blackbox.c
@@ -7,7 +7,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/bridges.c b/bridges.c
index 1694039..bd4b3ca 100644
--- a/bridges.c
+++ b/bridges.c
@@ -73,7 +73,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/cmake/testbuild.c b/cmake/testbuild.c
index 67a6879..137af2f 100644
--- a/cmake/testbuild.c
+++ b/cmake/testbuild.c
@@ -5,7 +5,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <errno.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include <sys/time.h>
 #include <sys/resource.h>
diff --git a/cube.c b/cube.c
index 3b4e975..1261730 100644
--- a/cube.c
+++ b/cube.c
@@ -7,7 +7,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/dominosa.c b/dominosa.c
index 35f6a56..801c1f1 100644
--- a/dominosa.c
+++ b/dominosa.c
@@ -48,7 +48,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/drawing.c b/drawing.c
index 5fb8a31..90f54f3 100644
--- a/drawing.c
+++ b/drawing.c
@@ -27,7 +27,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/fifteen.c b/fifteen.c
index 11e1a7b..53b06aa 100644
--- a/fifteen.c
+++ b/fifteen.c
@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/filling.c b/filling.c
index 6552d50..87b9d9e 100644
--- a/filling.c
+++ b/filling.c
@@ -58,7 +58,7 @@
 
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/flip.c b/flip.c
index 7170bb4..1112443 100644
--- a/flip.c
+++ b/flip.c
@@ -9,7 +9,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/flood.c b/flood.c
index 0ed8f06..da2317a 100644
--- a/flood.c
+++ b/flood.c
@@ -32,7 +32,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/galaxies.c b/galaxies.c
index 10c92d8..e3cc76e 100644
--- a/galaxies.c
+++ b/galaxies.c
@@ -80,7 +80,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/grid.c b/grid.c
index c2e08db..d2a3e13 100644
--- a/grid.c
+++ b/grid.c
@@ -13,7 +13,7 @@
 #include <ctype.h>
 #include <float.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/gtk.c b/gtk.c
index eab6980..ce792d3 100644
--- a/gtk.c
+++ b/gtk.c
@@ -13,7 +13,7 @@
 #include <stdarg.h>
 #include <string.h>
 #include <errno.h>
-#include <math.h>
+#include <tgmath.h>
 #include <unistd.h>
 
 #include <sys/time.h>
diff --git a/guess.c b/guess.c
index f359a99..55a30e8 100644
--- a/guess.c
+++ b/guess.c
@@ -7,7 +7,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/hat.c b/hat.c
index 0a2dd21..99babcc 100644
--- a/hat.c
+++ b/hat.c
@@ -12,7 +12,7 @@
  */
 
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/inertia.c b/inertia.c
index 1a958af..92747ed 100644
--- a/inertia.c
+++ b/inertia.c
@@ -12,7 +12,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/keen.c b/keen.c
index a414129..5624865 100644
--- a/keen.c
+++ b/keen.c
@@ -8,7 +8,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "latin.h"
diff --git a/lightup.c b/lightup.c
index 0cead04..816dd70 100644
--- a/lightup.c
+++ b/lightup.c
@@ -48,7 +48,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/loopgen.c b/loopgen.c
index e738d4a..d8f5e27 100644
--- a/loopgen.c
+++ b/loopgen.c
@@ -8,7 +8,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/loopy.c b/loopy.c
index fd86296..b7d91de 100644
--- a/loopy.c
+++ b/loopy.c
@@ -77,7 +77,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/magnets.c b/magnets.c
index 0669978..90157bb 100644
--- a/magnets.c
+++ b/magnets.c
@@ -37,7 +37,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/map.c b/map.c
index 23f6fe9..76b0518 100644
--- a/map.c
+++ b/map.c
@@ -15,7 +15,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/mines.c b/mines.c
index 6cd9674..09e3422 100644
--- a/mines.c
+++ b/mines.c
@@ -13,7 +13,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "tree234.h"
 #include "puzzles.h"
diff --git a/misc.c b/misc.c
index 659de83..2cefd36 100644
--- a/misc.c
+++ b/misc.c
@@ -3,7 +3,7 @@
  */
 
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
diff --git a/mosaic.c b/mosaic.c
index 080800c..5fb223e 100644
--- a/mosaic.c
+++ b/mosaic.c
@@ -14,7 +14,7 @@
 
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/net.c b/net.c
index e7c47bb..e3357ac 100644
--- a/net.c
+++ b/net.c
@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/netslide.c b/netslide.c
index 2c10a37..a0b00b4 100644
--- a/netslide.c
+++ b/netslide.c
@@ -9,7 +9,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/nullgame.c b/nullgame.c
index c539d1b..c5ad0c9 100644
--- a/nullgame.c
+++ b/nullgame.c
@@ -16,7 +16,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/pattern.c b/pattern.c
index 8f88283..d8f050b 100644
--- a/pattern.c
+++ b/pattern.c
@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/pearl.c b/pearl.c
index 2cbaf0f..74ab471 100644
--- a/pearl.c
+++ b/pearl.c
@@ -36,7 +36,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "grid.h"
diff --git a/pegs.c b/pegs.c
index cd696f6..0639eb3 100644
--- a/pegs.c
+++ b/pegs.c
@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/penrose.c b/penrose.c
index df0b72e..6ae9756 100644
--- a/penrose.c
+++ b/penrose.c
@@ -9,7 +9,7 @@
 
 #include <assert.h>
 #include <string.h>
-#include <math.h>
+#include <tgmath.h>
 #include <stdio.h>
 
 #include "puzzles.h" /* for malloc routines, and PI */
diff --git a/range.c b/range.c
index 293b6cb..45ab10b 100644
--- a/range.c
+++ b/range.c
@@ -58,7 +58,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/rect.c b/rect.c
index 1dffacb..40bc846 100644
--- a/rect.c
+++ b/rect.c
@@ -26,7 +26,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/samegame.c b/samegame.c
index fd5cfad..54e73d5 100644
--- a/samegame.c
+++ b/samegame.c
@@ -68,7 +68,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/signpost.c b/signpost.c
index 70b444a..aeb32ea 100644
--- a/signpost.c
+++ b/signpost.c
@@ -8,7 +8,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/singles.c b/singles.c
index a4c901d..3fc9d5a 100644
--- a/singles.c
+++ b/singles.c
@@ -58,7 +58,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "latin.h"
diff --git a/sixteen.c b/sixteen.c
index 6029b8d..7dbb9c3 100644
--- a/sixteen.c
+++ b/sixteen.c
@@ -10,7 +10,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/slant.c b/slant.c
index bcf02ee..a174011 100644
--- a/slant.c
+++ b/slant.c
@@ -28,7 +28,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/solo.c b/solo.c
index 6b2862f..ed1787b 100644
--- a/solo.c
+++ b/solo.c
@@ -87,7 +87,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #ifdef STANDALONE_SOLVER
 #include <stdarg.h>
diff --git a/tents.c b/tents.c
index f6b8544..47a0d11 100644
--- a/tents.c
+++ b/tents.c
@@ -33,7 +33,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "matching.h"
diff --git a/towers.c b/towers.c
index 1e2647d..b3b1478 100644
--- a/towers.c
+++ b/towers.c
@@ -23,7 +23,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "latin.h"
diff --git a/tracks.c b/tracks.c
index 6b882e9..151f7fb 100644
--- a/tracks.c
+++ b/tracks.c
@@ -21,7 +21,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/twiddle.c b/twiddle.c
index 215d225..2c15617 100644
--- a/twiddle.c
+++ b/twiddle.c
@@ -11,7 +11,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/undead.c b/undead.c
index 833eb34..4ef8fe4 100644
--- a/undead.c
+++ b/undead.c
@@ -35,7 +35,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/unequal.c b/unequal.c
index 9c75d51..f50197b 100644
--- a/unequal.c
+++ b/unequal.c
@@ -21,7 +21,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "latin.h" /* contains typedef for digit */
diff --git a/unfinished/group.c b/unfinished/group.c
index 891c4e4..345deb5 100644
--- a/unfinished/group.c
+++ b/unfinished/group.c
@@ -31,7 +31,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "latin.h"
diff --git a/unfinished/numgame.c b/unfinished/numgame.c
index 849c83e..5de69a2 100644
--- a/unfinished/numgame.c
+++ b/unfinished/numgame.c
@@ -40,7 +40,7 @@
 #include <string.h>
 #include <limits.h>
 #include <assert.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/unfinished/separate.c b/unfinished/separate.c
index 9ffa632..fdeeb3d 100644
--- a/unfinished/separate.c
+++ b/unfinished/separate.c
@@ -94,7 +94,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/unfinished/slide.c b/unfinished/slide.c
index acddd93..a4cf168 100644
--- a/unfinished/slide.c
+++ b/unfinished/slide.c
@@ -32,7 +32,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"
diff --git a/unfinished/sokoban.c b/unfinished/sokoban.c
index 80596c2..a493bf4 100644
--- a/unfinished/sokoban.c
+++ b/unfinished/sokoban.c
@@ -58,7 +58,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/unruly.c b/unruly.c
index af84111..c791baf 100644
--- a/unruly.c
+++ b/unruly.c
@@ -47,7 +47,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 
diff --git a/untangle.c b/untangle.c
index cd1762f..558cce7 100644
--- a/untangle.c
+++ b/untangle.c
@@ -32,7 +32,7 @@
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h>
-#include <math.h>
+#include <tgmath.h>
 
 #include "puzzles.h"
 #include "tree234.h"