diff --git a/src/_webp.c b/src/_webp.c
index a1b4dbc1a25..d46d3fc789c 100644
--- a/src/_webp.c
+++ b/src/_webp.c
@@ -873,7 +873,7 @@ WebPDecode_wrapper(PyObject *self, PyObject *args) {
 // Return the decoder's version number, packed in hexadecimal using 8bits for
 // each of major/minor/revision. E.g: v2.5.7 is 0x020507.
 PyObject *
-WebPDecoderVersion_wrapper() {
+WebPDecoderVersion_wrapper(PyObject *self, PyObject *Py_UNUSED(args)) {
     return Py_BuildValue("i", WebPGetDecoderVersion());
 }
 
@@ -901,7 +901,7 @@ WebPDecoderBuggyAlpha(void) {
 }
 
 PyObject *
-WebPDecoderBuggyAlpha_wrapper() {
+WebPDecoderBuggyAlpha_wrapper(PyObject *self, PyObject *Py_UNUSED(args)) {
     return Py_BuildValue("i", WebPDecoderBuggyAlpha());
 }
 
diff --git a/src/display.c b/src/display.c
index ef2ff3754f1..6b66ddafb87 100644
--- a/src/display.c
+++ b/src/display.c
@@ -427,7 +427,6 @@ PyImaging_GrabScreenWin32(PyObject *self, PyObject *args) {
 
 PyObject *
 PyImaging_GrabClipboardWin32(PyObject *self, PyObject *args) {
-    int clip;
     HANDLE handle = NULL;
     int size;
     void *data;
diff --git a/src/libImaging/Draw.c b/src/libImaging/Draw.c
index 0ccf22d58dd..c83d05afa8b 100644
--- a/src/libImaging/Draw.c
+++ b/src/libImaging/Draw.c
@@ -34,6 +34,7 @@
 
 #include "Imaging.h"
 
+#define _USE_MATH_DEFINES
 #include <math.h>
 #include <stdint.h>
 
diff --git a/src/libImaging/Imaging.h b/src/libImaging/Imaging.h
index afcd2229bde..43350f07b4f 100644
--- a/src/libImaging/Imaging.h
+++ b/src/libImaging/Imaging.h
@@ -16,10 +16,6 @@
 extern "C" {
 #endif
 
-#ifndef M_PI
-#define M_PI 3.1415926535897932384626433832795
-#endif
-
 /* -------------------------------------------------------------------- */
 
 /*
diff --git a/src/libImaging/QuantOctree.c b/src/libImaging/QuantOctree.c
index 5e79bce358a..cc96bb2fba1 100644
--- a/src/libImaging/QuantOctree.c
+++ b/src/libImaging/QuantOctree.c
@@ -367,7 +367,7 @@ map_image_pixels(
     uint32_t nPixels,
     const ColorCube lookupCube,
     uint32_t *pixelArray) {
-    long i;
+    unsigned long i;
     for (i = 0; i < nPixels; i++) {
         pixelArray[i] = lookup_color(lookupCube, &pixelData[i]);
     }
@@ -393,7 +393,7 @@ quantize_octree(
     ColorBucket paletteBucketsFine = NULL;
     ColorBucket paletteBuckets = NULL;
     uint32_t *qp = NULL;
-    long i;
+    unsigned long i;
     unsigned long nCoarseColors, nFineColors, nAlreadySubtracted;
     const unsigned int *cubeBits;
 
diff --git a/src/libImaging/Resample.c b/src/libImaging/Resample.c
index cf79d8a4e4d..9da13352460 100644
--- a/src/libImaging/Resample.c
+++ b/src/libImaging/Resample.c
@@ -1,5 +1,6 @@
 #include "Imaging.h"
 
+#define _USE_MATH_DEFINES
 #include <math.h>
 
 #define ROUND_UP(f) ((int)((f) >= 0.0 ? (f) + 0.5F : (f)-0.5F))
diff --git a/src/libImaging/TiffDecode.c b/src/libImaging/TiffDecode.c
index e3b81590ec2..a8a2d2b24e1 100644
--- a/src/libImaging/TiffDecode.c
+++ b/src/libImaging/TiffDecode.c
@@ -973,7 +973,10 @@ ImagingLibTiffEncode(Imaging im, ImagingCodecState state, UINT8 *buffer, int byt
     }
 
     if (state->state == 1 && !clientstate->fp) {
-        int read = (int)_tiffReadProc(clientstate, (tdata_t)buffer, (tsize_t)bytes);
+        int read = (int)_tiffReadProc(
+            (thandle_t)clientstate,
+            (tdata_t)buffer,
+            (tsize_t)bytes);
         TRACE(
             ("Buffer: %p: %c%c%c%c\n",
              buffer,