diff --git a/c/src/include/macros.h b/c/src/include/macros.h
index 3688efca..4e636451 100644
--- a/c/src/include/macros.h
+++ b/c/src/include/macros.h
@@ -66,7 +66,7 @@
 #endif
 
 #ifndef swap
-    #define swap(x, y, T) do { T SWAP = x; x = y; y = SWAP; } while (0)
+    #define swap(x, y) do { typeof(x) SWAP = x; x = y; y = SWAP; } while (0)
 #endif
 
 #if !(CL_COMPILER || TCC_COMPILER)
diff --git a/c/src/p0025.c b/c/src/p0025.c
index d1274c39..d26b6eeb 100644
--- a/c/src/p0025.c
+++ b/c/src/p0025.c
@@ -36,7 +36,7 @@ unsigned long long p0025() {
     BCD_int a = BCD_one, b = BCD_one;
     while (b.decimal_digits < 1000) {
         iadd_bcd(&a, b);
-        swap(a, b, BCD_int);
+        swap(a, b);
         answer++;
     }
     free_BCD_int(a);
diff --git a/docs/src/c/lib/macros.rst b/docs/src/c/lib/macros.rst
index 3303c5d9..77162ce4 100644
--- a/docs/src/c/lib/macros.rst
+++ b/docs/src/c/lib/macros.rst
@@ -30,7 +30,11 @@ View source code :source:`c/src/include/macros.h`
 .. c:macro:: max(a, b)
              min(a, b)
 
-    If these were not already defined, this header makes them
+    If these were not already defined, this header makes them.
+
+.. c:macro:: swap(x, y)
+
+    Swap the names of two variables of the same type.
 
 .. c:macro:: likely(x)
              unlikely(x)