diff --git a/kernel/x86_64/ddot.c b/kernel/x86_64/ddot.c
index f3b9ee701..569ed2416 100644
--- a/kernel/x86_64/ddot.c
+++ b/kernel/x86_64/ddot.c
@@ -159,7 +159,7 @@ static int dot_thread_function(BLASLONG n, BLASLONG dummy0,
 
 extern int blas_level1_thread_with_return_value(int mode, BLASLONG m, BLASLONG n,
         BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb,
-        void *c, BLASLONG ldc, int (*function)(), int nthreads);
+        void *c, BLASLONG ldc, int (*function)(void), int nthreads);
 #endif
 
 FLOAT CNAME(BLASLONG n, FLOAT *x, BLASLONG inc_x, FLOAT *y, BLASLONG inc_y)
diff --git a/kernel/x86_64/drot.c b/kernel/x86_64/drot.c
index 40c9cf19d..6fdf4ae56 100644
--- a/kernel/x86_64/drot.c
+++ b/kernel/x86_64/drot.c
@@ -169,7 +169,7 @@ static int rot_thread_function(blas_arg_t *args)
     return 0;
 }
 
-extern int blas_level1_thread(int mode, BLASLONG m, BLASLONG n, BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb, void *c, BLASLONG ldc, int (*function)(), int nthreads);
+extern int blas_level1_thread(int mode, BLASLONG m, BLASLONG n, BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb, void *c, BLASLONG ldc, int (*function)(void), int nthreads);
 #endif
 int CNAME(BLASLONG n, FLOAT *x, BLASLONG inc_x, FLOAT *y, BLASLONG inc_y, FLOAT c, FLOAT s)
 {
diff --git a/kernel/x86_64/srot.c b/kernel/x86_64/srot.c
index a49544616..05724b427 100644
--- a/kernel/x86_64/srot.c
+++ b/kernel/x86_64/srot.c
@@ -171,7 +171,7 @@ static int rot_thread_function(blas_arg_t *args)
     return 0;
 }
 
-extern int blas_level1_thread(int mode, BLASLONG m, BLASLONG n, BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb, void *c, BLASLONG ldc, int (*function)(), int nthreads);
+extern int blas_level1_thread(int mode, BLASLONG m, BLASLONG n, BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb, void *c, BLASLONG ldc, int (*function)(void), int nthreads);
 #endif
 int CNAME(BLASLONG n, FLOAT *x, BLASLONG inc_x, FLOAT *y, BLASLONG inc_y, FLOAT c, FLOAT s)
 {
diff --git a/kernel/x86_64/zdot.c b/kernel/x86_64/zdot.c
index 72a712a9e..51efa2dfe 100644
--- a/kernel/x86_64/zdot.c
+++ b/kernel/x86_64/zdot.c
@@ -92,7 +92,7 @@ static void zdot_kernel_8(BLASLONG n, FLOAT *x, FLOAT *y, FLOAT *d)
 #if defined(SMP)
 extern int blas_level1_thread_with_return_value(int mode, BLASLONG m, BLASLONG n,
         BLASLONG k, void *alpha, void *a, BLASLONG lda, void *b, BLASLONG ldb,
-        void *c, BLASLONG ldc, int (*function)(), int nthreads);
+        void *c, BLASLONG ldc, int (*function)(void), int nthreads);
 #endif