diff --git a/src/Makefile.am b/src/Makefile.am
index 6ca5a13..f82849b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -17,7 +17,7 @@
 #  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-AM_CFLAGS = -Wall # -Werror
+AM_CFLAGS = -Wall # -Werror -Wdouble-promotion
 
 AM_CPPFLAGS = $(DEPS_CFLAGS)
 
diff --git a/src/fsk.c b/src/fsk.c
index bdeca61..5020dd0 100644
--- a/src/fsk.c
+++ b/src/fsk.c
@@ -20,7 +20,7 @@
 
 #include <stdlib.h>
 #include <string.h>
-#include <math.h>	// fabs, hypotf
+#include <math.h>	// fabsf, hypotf
 #include <float.h>	// FLT_EPSILON
 #include <errno.h>
 #include <stdio.h>
@@ -49,7 +49,7 @@ fsk_plan_new(
 #ifdef USE_FFT
     fskp->band_width = filter_bw;
 
-    float fft_half_bw = fskp->band_width / 2.0;
+    float fft_half_bw = fskp->band_width / 2.0f;
     fskp->fftsize = (sample_rate + fft_half_bw) / fskp->band_width;
     fskp->nbands = fskp->fftsize / 2 + 1;
 
@@ -129,7 +129,7 @@ fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
 
     memcpy(fskp->fftin, samples, bit_nsamples * sizeof(float));
 
-    float magscalar = 2.0 / (float)bit_nsamples;
+    float magscalar = 2.0f / (float)bit_nsamples;
 
 #if 0
     //// apodization window
@@ -148,7 +148,7 @@ fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
 	float zoff = 0.0; // 0.5  // FIXME which is it??
 	unsigned int z = bit_nsamples /* not -1  ... explain */;
 	float w = a0
-		- a1 * cos((2.0*M_PI*((float)i+zoff)) / z);
+		- a1 * cosf((2.0*M_PI*((float)i+zoff)) / z);
 	fskp->fftin[i] *= w;
     }
 #endif
@@ -180,7 +180,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
 	int n_bits, const char *expect_bits_string,
 	unsigned long long *bits_outp, float *ampl_outp )
 {
-    unsigned int bit_nsamples = (float)(samples_per_bit + 0.5);
+    unsigned int bit_nsamples = (float)(samples_per_bit + 0.5f);
 
     unsigned int	bit_values[64];
     float		bit_sig_mags[64];
@@ -201,7 +201,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
 	    continue;
 	assert( expect_bits[bitnum] == '1' || expect_bits[bitnum] == '0' );
 
-	bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5);
+	bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5f);
 	debug_log( " bit# %2u @ %7u: ", bitnum, bit_begin_sample);
 	fsk_bit_analyze(fskp, samples+bit_begin_sample, bit_nsamples,
 		&bit_values[bitnum],
@@ -236,7 +236,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
      * diff between start bit and stop bit strength not be "large". */
     float s_mag = bit_sig_mags[1]; // start bit
     float p_mag = bit_sig_mags[n_bits-1]; // stop bit
-    if ( fabs(s_mag-p_mag) > (s_mag * FSK_AVOID_TRANSIENTS) ) {
+    if ( fabsf(s_mag-p_mag) > (s_mag * FSK_AVOID_TRANSIENTS) ) {
 	debug_log(" avoid transient\n");
 	return 0.0;
     }
@@ -246,7 +246,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
     for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
 	if ( expect_bits[bitnum] != 'd' )
 	    continue;
-	bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5);
+	bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5f);
 	debug_log( " bit# %2u @ %7u: ", bitnum, bit_begin_sample);
 	fsk_bit_analyze(fskp, samples+bit_begin_sample, bit_nsamples,
 		&bit_values[bitnum],
@@ -306,7 +306,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
     for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
 	float avg_bit_sig_other;
 	avg_bit_sig_other = bit_values[bitnum] ? avg_mark_sig : avg_space_sig;
-	divergence += fabs(bit_sig_mags[bitnum] - avg_bit_sig_other)
+	divergence += fabsf(bit_sig_mags[bitnum] - avg_bit_sig_other)
 					/ avg_bit_sig_other;
     }
     divergence *= 2;
@@ -333,7 +333,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
 
 #if CONFIDENCE_ALGO == 6
     // Frame confidence is the frame ( SNR * consistency )
-    confidence = snr * (1.0 - divergence);
+    confidence = snr * (1.0f - divergence);
 #else
     // Frame confidence is the frame SNR
     confidence = snr;
@@ -388,8 +388,8 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
 	else
 	    normalized_bit_str = bit_strengths[bitnum] - v_space;
 	debug_log("%.2f  ", normalized_bit_str);
-	// float divergence = fabs(1.0 - normalized_bit_str);
-	float divergence = fabs(normalized_bit_str);
+	// float divergence = fabsf(1.0 - normalized_bit_str);
+	float divergence = fabsf(normalized_bit_str);
 	if ( worst_divergence < divergence )
 	    worst_divergence = divergence;
     }
@@ -423,7 +423,7 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
     for ( bitnum=0; bitnum<n_bits-1; bitnum++ )
     {
 	float normalized_bit_str = bit_strengths[bitnum] / v;
-	float divergence = fabs(1.0 - normalized_bit_str);
+	float divergence = fabsf(1.0 - normalized_bit_str);
 	if ( worst_divergence < divergence )
 	    worst_divergence = divergence;
     }
@@ -548,7 +548,7 @@ fsk_detect_carrier(fsk_plan *fskp, float *samples, unsigned int nsamples,
     bzero(fskp->fftin, (fskp->fftsize * sizeof(float) * pa_nchannels));
     memcpy(fskp->fftin, samples, nsamples * sizeof(float));
     fftwf_execute(fskp->fftplan);
-    float magscalar = 1.0 / ((float)nsamples/2.0);
+    float magscalar = 1.0f / ((float)nsamples/2.0f);
     float max_mag = 0.0;
     int max_mag_band = -1;
     int i = 1;	/* start detection at the first non-DC band */
diff --git a/src/minimodem.c b/src/minimodem.c
index 9257b33..0251d03 100644
--- a/src/minimodem.c
+++ b/src/minimodem.c
@@ -125,7 +125,7 @@ static void fsk_transmit_stdin(
 	)
 {
     size_t sample_rate = simpleaudio_get_rate(sa_out);
-    size_t bit_nsamples = sample_rate / data_rate + 0.5;
+    size_t bit_nsamples = sample_rate / data_rate + 0.5f;
 
     tx_sa_out = sa_out;
     tx_bfsk_mark_f = bfsk_mark_f;
@@ -134,7 +134,7 @@ static void fsk_transmit_stdin(
     // one-shot
     struct itimerval itv = {
 	{0, 0},						// it_interval
-	{0, 1000000/(float)(data_rate+data_rate*0.03) }	// it_value
+	{0, 1000000/(float)(data_rate+data_rate*0.03f)}	// it_value
     };
 
     struct itimerval itv_zero = {
@@ -251,21 +251,21 @@ report_no_carrier( fsk_plan *fskp,
 		nbits_decoded * sample_rate / (float)carrier_nsamples;
     fprintf(stderr, "\n### NOCARRIER ndata=%u confidence=%.3f ampl=%.3f bps=%.2f",
 	    nframes_decoded,
-	    confidence_total / nframes_decoded,
-	    amplitude_total / nframes_decoded,
-	    throughput_rate);
+	    (double)(confidence_total / nframes_decoded),
+	    (double)(amplitude_total / nframes_decoded),
+	    (double)(throughput_rate));
 #if 0
     fprintf(stderr, " bits*sr=%llu rate*nsamp=%llu",
 	    (unsigned long long)(nbits_decoded * sample_rate + 0.5),
 	    (unsigned long long)(bfsk_data_rate * carrier_nsamples) );
 #endif
-    if ( (unsigned long long)(nbits_decoded * sample_rate + 0.5) == (unsigned long long)(bfsk_data_rate * carrier_nsamples) ) {
+    if ( (unsigned long long)(nbits_decoded * sample_rate + 0.5f) == (unsigned long long)(bfsk_data_rate * carrier_nsamples) ) {
 	fprintf(stderr, " (rate perfect) ###\n");
     } else {
 	float throughput_skew = (throughput_rate - bfsk_data_rate)
 			    / bfsk_data_rate;
 	fprintf(stderr, " (%.1f%% %s) ###\n",
-		fabs(throughput_skew) * 100.0,
+		(double)(fabsf(throughput_skew) * 100.0f),
 		signbit(throughput_skew) ? "slow" : "fast"
 		);
     }
@@ -444,7 +444,7 @@ build_expect_bits_string( char *expect_bits_string,
 	char start_bit_value = invert_start_stop ? '1' : '0';
 	char stop_bit_value = invert_start_stop ? '0' : '1';
 	int j = 0;
-	if ( bfsk_nstopbits != 0.0 )
+	if ( bfsk_nstopbits != 0.0f )
 	    expect_bits_string[j++] = stop_bit_value;
 	int i;
 	// Nb. only integer number of start bits works (for rx)
@@ -456,7 +456,7 @@ build_expect_bits_string( char *expect_bits_string,
 	    else
 		expect_bits_string[j] = 'd';
 	}
-	if ( bfsk_nstopbits != 0.0 )
+	if ( bfsk_nstopbits != 0.0f )
 	    expect_bits_string[j++] = stop_bit_value;
 	expect_bits_string[j] = 0;
 
@@ -660,7 +660,7 @@ main( int argc, char*argv[] )
 			    tx_amplitude = FLT_EPSILON;
 			else
 			    tx_amplitude = atof(optarg);
-			assert( tx_amplitude > 0.0 );
+			assert( tx_amplitude > 0.0f );
 			break;
 	    case 'M':
 			bfsk_mark_f = atof(optarg);
@@ -798,7 +798,7 @@ main( int argc, char*argv[] )
 	    fprintf(stderr, "E: callerid --tx mode is not supported.\n");
 	    return 1;
 	}
-	if ( carrier_autodetect_threshold > 0.0 )
+	if ( carrier_autodetect_threshold > 0.0f )
 	    fprintf(stderr, "W: callerid with --auto-carrier is not recommended.\n");
 	bfsk_databits_decode = databits_decode_callerid;
 	bfsk_data_rate = 1200;
@@ -826,7 +826,7 @@ main( int argc, char*argv[] )
 	if ( bfsk_n_data_bits == 0 )
 	    bfsk_n_data_bits = 8;
     }
-    if ( bfsk_data_rate == 0.0 )
+    if ( bfsk_data_rate == 0.0f )
 	usage();
 
 
@@ -964,7 +964,7 @@ main( int argc, char*argv[] )
 
     sample_rate = simpleaudio_get_rate(sa);
 
-    if ( rxnoise_factor != 0.0 )
+    if ( rxnoise_factor != 0.0f )
 	simpleaudio_set_rxnoise(sa, rxnoise_factor);
 
     /*
@@ -1035,19 +1035,19 @@ main( int argc, char*argv[] )
     // for encodings without start/stop bits:
     //     MUST be <= 0.5 or we may accidentally skip a bit
     //
-    assert( fsk_frame_overscan >= 0.0 && fsk_frame_overscan < 1.0 );
+    assert( fsk_frame_overscan >= 0.0f && fsk_frame_overscan < 1.0f );
 
     // ensure that we overscan at least a single sample
     unsigned int nsamples_overscan
-			= nsamples_per_bit * fsk_frame_overscan + 0.5;
-    if ( fsk_frame_overscan > 0.0 && nsamples_overscan == 0 )
+			= nsamples_per_bit * fsk_frame_overscan + 0.5f;
+    if ( fsk_frame_overscan > 0.0f && nsamples_overscan == 0 )
 	nsamples_overscan = 1;
     debug_log("fsk_frame_overscan=%f nsamples_overscan=%u\n",
 	    fsk_frame_overscan, nsamples_overscan);
 
     // n databits plus bfsk_startbit start bits plus bfsk_nstopbit stop bits:
     float frame_n_bits = bfsk_n_data_bits + bfsk_nstartbits + bfsk_nstopbits;
-    unsigned int frame_nsamples = nsamples_per_bit * frame_n_bits + 0.5;
+    unsigned int frame_nsamples = nsamples_per_bit * frame_n_bits + 0.5f;
 
     char expect_data_string_buffer[64];
     if (expect_data_string == NULL) {
@@ -1115,7 +1115,7 @@ main( int argc, char*argv[] )
 
 	/* Auto-detect carrier frequency */
 	static int carrier_band = -1;
-	if ( carrier_autodetect_threshold > 0.0 && carrier_band < 0 ) {
+	if ( carrier_autodetect_threshold > 0.0f && carrier_band < 0 ) {
 	    unsigned int i;
 	    float nsamples_per_scan = nsamples_per_bit;
 	    if ( nsamples_per_scan > fskp->fftsize )
@@ -1137,7 +1137,7 @@ main( int argc, char*argv[] )
 	    }
 
 	    // default negative shift -- reasonable?
-	    int b_shift = - (float)(autodetect_shift + fskp->band_width/2.0)
+	    int b_shift = - (float)(autodetect_shift + fskp->band_width/2.0f)
 						/ fskp->band_width;
 	    if ( bfsk_inverted_freqs )
 		b_shift *= -1;
@@ -1172,7 +1172,7 @@ main( int argc, char*argv[] )
 	// 2. allows us to track slightly slow signals
 	unsigned int try_max_nsamples;
 	if ( carrier )
-	    try_max_nsamples = nsamples_per_bit * 0.75 + 0.5;
+	    try_max_nsamples = nsamples_per_bit * 0.75f + 0.5f;
 	else
 	    try_max_nsamples = nsamples_per_bit;
 	try_max_nsamples += nsamples_overscan;
@@ -1212,7 +1212,7 @@ main( int argc, char*argv[] )
 
 	int do_refine_frame = 0;
 
-	if ( confidence < peak_confidence * 0.75 ) {
+	if ( confidence < peak_confidence * 0.75f ) {
 	    do_refine_frame = 1;
 	    debug_log(" ... do_refine_frame rescan (confidence %.3f << %.3f peak)\n", confidence, peak_confidence);
 	    peak_confidence = 0;
@@ -1220,7 +1220,7 @@ main( int argc, char*argv[] )
 
 	// no-confidence if amplitude drops abruptly to < 25% of the
 	// track_amplitude, which follows amplitude with hysteresis
-	if ( amplitude < track_amplitude * 0.25 ) {
+	if ( amplitude < track_amplitude * 0.25f ) {
 	    confidence = 0;
 	}
 
@@ -1273,12 +1273,12 @@ main( int argc, char*argv[] )
 	    if ( !quiet_mode ) {
 		if ( bfsk_data_rate >= 100 )
 		    fprintf(stderr, "### CARRIER %u @ %.1f Hz ",
-			    (unsigned int)(bfsk_data_rate + 0.5),
-			    fskp->b_mark * fskp->band_width);
+			    (unsigned int)(bfsk_data_rate + 0.5f),
+			    (double)(fskp->b_mark * fskp->band_width));
 		else
 		    fprintf(stderr, "### CARRIER %.2f @ %.1f Hz ",
-			    bfsk_data_rate,
-			    fskp->b_mark * fskp->band_width);
+			    (double)(bfsk_data_rate),
+			    (double)(fskp->b_mark * fskp->band_width));
 	    }
 
 	    if ( !quiet_mode )
@@ -1349,7 +1349,7 @@ main( int argc, char*argv[] )
 		    frame_start_sample, advance);
 
 	// chop off the prev_stop bit
-	if ( bfsk_nstopbits != 0.0 )
+	if ( bfsk_nstopbits != 0.0f )
 	    bits = bits >> 1;
 
 
diff --git a/src/simple-tone-generator.c b/src/simple-tone-generator.c
index 80bc108..f7f1151 100644
--- a/src/simple-tone-generator.c
+++ b/src/simple-tone-generator.c
@@ -49,15 +49,15 @@ simpleaudio_tone_init( unsigned int new_sin_table_len, float mag )
 	}
 
 	unsigned int i;
-	unsigned short mag_s = 32767.0 * tone_mag + 0.5f;
+	unsigned short mag_s = 32767.0f * tone_mag + 0.5f;
 	if ( tone_mag > 1.0f ) // clamp to 1.0 to avoid overflow
 	    mag_s = 32767;
 	if ( mag_s < 1 ) // "short epsilon"
 	    mag_s = 1;
 	for ( i=0; i<sin_table_len; i++ )
-	    sin_table_short[i] = lroundf( mag_s * sin(M_PI*2.0*(float)i/sin_table_len) );
+	    sin_table_short[i] = lroundf( mag_s * sinf((float)M_PI*2*i/sin_table_len) );
 	for ( i=0; i<sin_table_len; i++ )
-	    sin_table_float[i] = tone_mag * sinf(M_PI*2.0*(float)i/sin_table_len);
+	    sin_table_float[i] = tone_mag * sinf((float)M_PI*2*i/sin_table_len);
 
     } else {
 	if ( sin_table_short ) {
@@ -116,7 +116,7 @@ simpleaudio_tone(simpleaudio *sa_out, float tone_freq, size_t nsamples_dur)
 	float wave_nsamples = simpleaudio_get_rate(sa_out) / tone_freq;
 	size_t i;
 
-#define TURNS_TO_RADIANS(t)	( M_PI*2.0 * (t) )
+#define TURNS_TO_RADIANS(t)	( (float)M_PI*2 * (t) )
 
 #define SINE_PHASE_TURNS	( (float)i/wave_nsamples + sa_tone_cphase )
 #define SINE_PHASE_RADIANS	TURNS_TO_RADIANS(SINE_PHASE_TURNS)
@@ -143,7 +143,7 @@ simpleaudio_tone(simpleaudio *sa_out, float tone_freq, size_t nsamples_dur)
 			for ( i=0; i<nsamples_dur; i++ )
 			    short_buf[i] = sin_lu_short(SINE_PHASE_TURNS);
 		    } else {
-			unsigned short mag_s = 32767.0 * tone_mag + 0.5f;
+			unsigned short mag_s = 32767.0f * tone_mag + 0.5f;
 			if ( tone_mag > 1.0f ) // clamp to 1.0 to avoid overflow
 			    mag_s = 32767;
 			if ( mag_s < 1 ) // "short epsilon"
diff --git a/src/simpleaudio-sndfile.c b/src/simpleaudio-sndfile.c
index a4da348..d7c4f03 100644
--- a/src/simpleaudio-sndfile.c
+++ b/src/simpleaudio-sndfile.c
@@ -61,12 +61,12 @@ sa_sndfile_read( simpleaudio *sa, void *buf, size_t nframes )
 	return -1;
     }
 
-    if ( sa->rxnoise != 0.0 ) {
+    if ( sa->rxnoise != 0.0f ) {
 	int i;
 	float *fbuf = buf;
 	float f = sa->rxnoise * 2;
 	for ( i=0; i<nframes; i++ )
-	    fbuf[i] += (drand48() - 0.5) * f;
+	    fbuf[i] += (rand()/RAND_MAX - 0.5f) * f;
     }
 
     // fprintf(stderr, "sf_read: nframes=%ld n=%d\n", nframes, n);