diff --git a/dsf.c b/dsf.c
index aa22392..4f3abf0 100644
--- a/dsf.c
+++ b/dsf.c
@@ -15,7 +15,8 @@
     int *equal_elements = snewn(size, int);
     int *inverse_elements = snewn(size, int);
     int printed_count = 0, equal_count, inverse_count;
-    int i, n, inverse;
+    int i, n;
+    bool inverse;
 
     memset(printed_elements, -1, sizeof(int) * size);
 
@@ -99,10 +100,10 @@ int dsf_size(int *dsf, int index) {
     return dsf[dsf_canonify(dsf, index)] >> 2;
 }
 
-int edsf_canonify(int *dsf, int index, int *inverse_return)
+int edsf_canonify(int *dsf, int index, bool *inverse_return)
 {
     int start_index = index, canonical_index;
-    int inverse = 0;
+    bool inverse = false;
 
 /*    fprintf(stderr, "dsf = %p\n", dsf); */
 /*    fprintf(stderr, "Canonify %2d\n", index); */
@@ -141,9 +142,9 @@ int edsf_canonify(int *dsf, int index, int *inverse_return)
     return index;
 }
 
-void edsf_merge(int *dsf, int v1, int v2, int inverse)
+void edsf_merge(int *dsf, int v1, int v2, bool inverse)
 {
-    int i1, i2;
+    bool i1, i2;
 
 /*    fprintf(stderr, "dsf = %p\n", dsf); */
 /*    fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */
diff --git a/loopy.c b/loopy.c
index 708f188..7e83e66 100644
--- a/loopy.c
+++ b/loopy.c
@@ -1197,15 +1197,15 @@ static int merge_dots(solver_state *sstate, int edge_index)
 }
 
 /* Merge two lines because the solver has deduced that they must be either
- * identical or opposite.   Returns TRUE if this is new information, otherwise
- * FALSE. */
-static int merge_lines(solver_state *sstate, int i, int j, int inverse
+ * identical or opposite.   Returns true if this is new information, otherwise
+ * false. */
+static int merge_lines(solver_state *sstate, int i, int j, bool inverse
 #ifdef SHOW_WORKING
                        , const char *reason
 #endif
 		       )
 {
-    int inv_tmp;
+    bool inv_tmp;
 
     assert(i < sstate->state->game_grid->num_edges);
     assert(j < sstate->state->game_grid->num_edges);
@@ -1931,7 +1931,8 @@ static int face_setall_identical(solver_state *sstate, int face_index,
     grid_face *f = g->faces + face_index;
     int N = f->order;
     int i, j;
-    int can1, can2, inv1, inv2;
+    int can1, can2;
+    bool inv1, inv2;
 
     for (i = 0; i < N; i++) {
         int line1_index = f->edges[i] - g->edges;
@@ -1996,7 +1997,7 @@ static int parity_deductions(solver_state *sstate,
     } else if (unknown_count == 3) {
         int e[3];
         int can[3]; /* canonical edges */
-        int inv[3]; /* whether can[x] is inverse to e[x] */
+        bool inv[3]; /* whether can[x] is inverse to e[x] */
         find_unknowns(state, edge_list, 3, e);
         can[0] = edsf_canonify(linedsf, e[0], inv);
         can[1] = edsf_canonify(linedsf, e[1], inv+1);
@@ -2019,7 +2020,7 @@ static int parity_deductions(solver_state *sstate,
     } else if (unknown_count == 4) {
         int e[4];
         int can[4]; /* canonical edges */
-        int inv[4]; /* whether can[x] is inverse to e[x] */
+        bool inv[4]; /* whether can[x] is inverse to e[x] */
         find_unknowns(state, edge_list, 4, e);
         can[0] = edsf_canonify(linedsf, e[0], inv);
         can[1] = edsf_canonify(linedsf, e[1], inv+1);
@@ -2627,7 +2628,8 @@ static int linedsf_deductions(solver_state *sstate)
             int dline_index = dline_index_from_dot(g, d, j);
             int line1_index;
             int line2_index;
-            int can1, can2, inv1, inv2;
+            int can1, can2;
+            bool inv1, inv2;
             int j2;
             line1_index = d->edges[j] - g->edges;
             if (state->lines[line1_index] != LINE_UNKNOWN)
@@ -2671,7 +2673,8 @@ static int linedsf_deductions(solver_state *sstate)
     /* If the state of a line is known, deduce the state of its canonical line
      * too, and vice versa. */
     for (i = 0; i < g->num_edges; i++) {
-        int can, inv;
+        int can;
+        bool inv;
         enum line_state s;
         can = edsf_canonify(sstate->linedsf, i, &inv);
         if (can == i)
diff --git a/puzzles.h b/puzzles.h
index 379be15..d6d9e51 100644
--- a/puzzles.h
+++ b/puzzles.h
@@ -435,16 +435,16 @@ void print_dsf(int *dsf, int size);
 /* Return the canonical element of the equivalence class containing element
  * val.  If 'inverse' is non-NULL, this function will put into it a flag
  * indicating whether the canonical element is inverse to val. */
-int edsf_canonify(int *dsf, int val, int *inverse);
+int edsf_canonify(int *dsf, int val, bool *inverse);
 int dsf_canonify(int *dsf, int val);
 int dsf_size(int *dsf, int val);
 
 /* Allow the caller to specify that two elements should be in the same
- * equivalence class.  If 'inverse' is TRUE, the elements are actually opposite
+ * equivalence class.  If 'inverse' is true, the elements are actually opposite
  * to one another in some sense.  This function will fail an assertion if the
  * caller gives it self-contradictory data, ie if two elements are claimed to
  * be both opposite and non-opposite. */
-void edsf_merge(int *dsf, int v1, int v2, int inverse);
+void edsf_merge(int *dsf, int v1, int v2, bool inverse);
 void dsf_merge(int *dsf, int v1, int v2);
 void dsf_init(int *dsf, int len);