diff --git a/examples/extern_C/README b/examples/extern_C/README
index 4bc0873..af9c2cd 100644
--- a/examples/extern_C/README
+++ b/examples/extern_C/README
@@ -7,5 +7,5 @@ This example show how to import an external function written in C in an Heptagon
 
 To make it work:
    heptc mathext.epi
-   heptc imports.ept
-   gcc -std=c99 -I . mathext.c imports_c/*.c -o imports
+   heptc -target c imports.ept
+   gcc -c -I /usr/local/lib/heptagon/c -I . mathext.c imports_c/*.c
diff --git a/examples/extern_C/mathext.c b/examples/extern_C/mathext.c
index 91495b1..1f1d9a3 100644
--- a/examples/extern_C/mathext.c
+++ b/examples/extern_C/mathext.c
@@ -1,21 +1,22 @@
 #include <math.h>
 #include "mathext.h"
 
-void mycos_step(float a, mycos_out *out)
+void Mathext__mycos_step(float a, Mathext__mycos_out *out)
 {
-  out->o = cos(a);
+  out->o = cosf(a);
 }
 
-void st_cos_reset(st_cos_mem *self)
+void Mathext__st_cos_reset(Mathext__st_cos_mem *self)
 {
+  int j;
   self->i = 0;
-  for(int j = 0; j < 100; ++j)
+  for(j = 0; j < 100; ++j)
     self->mem[j] = 0.0;
 }
 
-void st_cos_step(float a, st_cos_out *out, st_cos_mem *self)
+void Mathext__st_cos_step(float a, Mathext__st_cos_out *out, Mathext__st_cos_mem *self)
 {
   out->o = self->mem[self->i];
   self->i = (self->i+1) % 100;
-  self->mem[self->i] = cos(a);
+  self->mem[self->i] = cosf(a);
 }
diff --git a/examples/extern_C/mathext.h b/examples/extern_C/mathext.h
index f20f922..0c26319 100644
--- a/examples/extern_C/mathext.h
+++ b/examples/extern_C/mathext.h
@@ -2,24 +2,24 @@
 #define MATHEXT_H
 
 /* Example of a combinatorial function */
-typedef struct mycos_out {
+typedef struct Mathext__mycos_out {
   float o;
-} mycos_out;
+} Mathext__mycos_out;
 
-void mycos_step(float a, mycos_out *o);
+void Mathext__mycos_step(float a, Mathext__mycos_out *o);
 
 /* Example of a statefull function. */
-typedef struct st_cos_out {
+typedef struct Mathext__st_cos_out {
   float o;
-} st_cos_out;
+} Mathext__st_cos_out;
 
-typedef struct st_cos_mem {
+typedef struct Mathext__st_cos_mem {
   int i;
   float mem[100];
-} st_cos_mem;
+} Mathext__st_cos_mem;
 
-void st_cos_reset(st_cos_mem *self);
-void st_cos_step(float a, st_cos_out *out, st_cos_mem *self);
+void Mathext__st_cos_reset(Mathext__st_cos_mem *self);
+void Mathext__st_cos_step(float a, Mathext__st_cos_out *out, Mathext__st_cos_mem *self);
 
 #endif