diff --git a/library/ecjpake.c b/library/ecjpake.c
index de43ddb..d229311 100644
--- a/library/ecjpake.c
+++ b/library/ecjpake.c
@@ -962,6 +962,28 @@
     0xb4, 0x38, 0xf7, 0x19, 0xd3, 0xc4, 0xf3, 0x51
 };
 
+/*
+ * PRNG for test - !!!INSECURE NEVER USE IN PRODUCTION!!!
+ *
+ * This is the linear congruential generator from numerical recipes,
+ * except we only use the low byte as the output. See
+ * https://en.wikipedia.org/wiki/Linear_congruential_generator#Parameters_in_common_use
+ */
+static int self_test_rng( void *ctx, unsigned char *out, size_t len )
+{
+    static uint32_t state = 42;
+
+    (void) ctx;
+
+    for( size_t i = 0; i < len; i++ )
+    {
+        state = state * 1664525u + 1013904223u;
+        out[i] = (unsigned char) state;
+    }
+
+    return( 0 );
+}
+
 /* Load my private keys and generate the corresponding public keys */
 static int ecjpake_test_load( mbedtls_ecjpake_context *ctx,
                               const unsigned char *xm1, size_t len1,
@@ -972,9 +994,9 @@
     MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &ctx->xm1, xm1, len1 ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &ctx->xm2, xm2, len2 ) );
     MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &ctx->Xm1, &ctx->xm1,
-                                      &ctx->grp.G, NULL, NULL ) );
+                                      &ctx->grp.G, self_test_rng, NULL ) );
     MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &ctx->Xm2, &ctx->xm2,
-                                      &ctx->grp.G, NULL, NULL ) );
+                                      &ctx->grp.G, self_test_rng, NULL ) );
 
 cleanup:
     return( ret );