diff --git a/conn_pool_test.go b/conn_pool_test.go
index 6e1134e4..636569e4 100644
--- a/conn_pool_test.go
+++ b/conn_pool_test.go
@@ -479,7 +479,7 @@ func TestConnPoolQuery(t *testing.T) {
 	}
 
 	if rows.Err() != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	if rowCount != 10 {
@@ -528,7 +528,7 @@ func TestConnPoolQueryConcurrentLoad(t *testing.T) {
 			}
 
 			if rows.Err() != nil {
-				t.Fatalf("conn.Query failed: ", rows.Err())
+				t.Fatalf("conn.Query failed: %v", rows.Err())
 			}
 
 			if rowCount != 1000 {
diff --git a/conn_test.go b/conn_test.go
index cd61fc95..9049bd6f 100644
--- a/conn_test.go
+++ b/conn_test.go
@@ -543,7 +543,7 @@ func TestParseEnvLibpq(t *testing.T) {
 		for k, v := range savedEnv {
 			err := os.Setenv(k, v)
 			if err != nil {
-				t.Fatalf("Unable to restore environment:", err)
+				t.Fatalf("Unable to restore environment: %v", err)
 			}
 		}
 	}()
@@ -685,14 +685,14 @@ func TestParseEnvLibpq(t *testing.T) {
 		for _, n := range pgEnvvars {
 			err := os.Unsetenv(n)
 			if err != nil {
-				t.Fatalf("%s: Unable to clear environment:", tt.name, err)
+				t.Fatalf("%s: Unable to clear environment: %v", tt.name, err)
 			}
 		}
 
 		for k, v := range tt.envvars {
 			err := os.Setenv(k, v)
 			if err != nil {
-				t.Fatalf("%s: Unable to set environment:", tt.name, err)
+				t.Fatalf("%s: Unable to set environment: %v", tt.name, err)
 			}
 		}
 
@@ -1103,7 +1103,7 @@ func TestListenNotifyWhileBusyIsSafe(t *testing.T) {
 
 			rows, err := conn.Query("select generate_series(1,$1)", 100)
 			if err != nil {
-				t.Fatalf("conn.Query failed: ", err)
+				t.Fatalf("conn.Query failed: %v", err)
 			}
 
 			for rows.Next() {
@@ -1114,7 +1114,7 @@ func TestListenNotifyWhileBusyIsSafe(t *testing.T) {
 			}
 
 			if rows.Err() != nil {
-				t.Fatalf("conn.Query failed: ", err)
+				t.Fatalf("conn.Query failed: %v", err)
 			}
 
 			if sum != 5050 {
@@ -1317,7 +1317,7 @@ func TestCatchSimultaneousConnectionQueries(t *testing.T) {
 
 	rows1, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	defer rows1.Close()
 
@@ -1335,7 +1335,7 @@ func TestCatchSimultaneousConnectionQueryAndExec(t *testing.T) {
 
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	defer rows.Close()
 
diff --git a/helper_test.go b/helper_test.go
index 509edbc9..ed5a9644 100644
--- a/helper_test.go
+++ b/helper_test.go
@@ -34,7 +34,7 @@ func ensureConnValid(t *testing.T, conn *pgx.Conn) {
 
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	defer rows.Close()
 
@@ -46,7 +46,7 @@ func ensureConnValid(t *testing.T, conn *pgx.Conn) {
 	}
 
 	if rows.Err() != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	if rowCount != 10 {
diff --git a/hstore.go b/hstore.go
index 332ad4b7..a5d40cce 100644
--- a/hstore.go
+++ b/hstore.go
@@ -146,13 +146,13 @@ func ParseHstore(s string) (k []string, v []NullString, err error) {
 					case r == 'N':
 						state = hsNul
 					default:
-						err = fmt.Errorf("Invalid character '%s' after '=>', expecting '\"' or 'NULL'")
+						err = fmt.Errorf("Invalid character '%c' after '=>', expecting '\"' or 'NULL'", r)
 					}
 				default:
 					err = fmt.Errorf("Invalid character after '=', expecting '>'")
 				}
 			} else {
-				err = fmt.Errorf("Invalid character '%s' after value, expecting '='", r)
+				err = fmt.Errorf("Invalid character '%c' after value, expecting '='", r)
 			}
 		case hsVal:
 			switch r {
@@ -201,10 +201,10 @@ func ParseHstore(s string) (k []string, v []NullString, err error) {
 					r, end = p.Consume()
 					state = hsKey
 				default:
-					err = fmt.Errorf("Invalid character '%s' after ', ', expecting \"", r)
+					err = fmt.Errorf("Invalid character '%c' after ', ', expecting \"", r)
 				}
 			} else {
-				err = fmt.Errorf("Invalid character '%s' after value, expecting ','", r)
+				err = fmt.Errorf("Invalid character '%c' after value, expecting ','", r)
 			}
 		}
 
diff --git a/hstore_test.go b/hstore_test.go
index f556b55e..445d9ba5 100644
--- a/hstore_test.go
+++ b/hstore_test.go
@@ -169,7 +169,7 @@ func TestNullHstoreTranscode(t *testing.T) {
 			outValue, ok := result.Hstore[key]
 			if ok {
 				if inValue != outValue {
-					t.Errorf(`%s: Key %s mismatch - expected %s, received %s`, tt.description, key, inValue, outValue)
+					t.Errorf(`%s: Key %s mismatch - expected %v, received %v`, tt.description, key, inValue, outValue)
 				}
 			} else {
 				t.Errorf(`%s: Missing key %s`, tt.description, key)
diff --git a/query_test.go b/query_test.go
index 06df6c95..0a36f161 100644
--- a/query_test.go
+++ b/query_test.go
@@ -21,7 +21,7 @@ func TestConnQueryScan(t *testing.T) {
 
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	defer rows.Close()
 
@@ -33,7 +33,7 @@ func TestConnQueryScan(t *testing.T) {
 	}
 
 	if rows.Err() != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	if rowCount != 10 {
@@ -54,7 +54,7 @@ func TestConnQueryValues(t *testing.T) {
 
 	rows, err := conn.Query("select 'foo', n, null, n::oid from generate_series(1,$1) n", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	defer rows.Close()
 
@@ -80,7 +80,7 @@ func TestConnQueryValues(t *testing.T) {
 		}
 
 		if values[2] != nil {
-			t.Errorf(`Expected values[2] to be %d, but it was %d`, nil, values[2])
+			t.Errorf(`Expected values[2] to be %v, but it was %d`, nil, values[2])
 		}
 
 		if values[3] != pgx.Oid(rowCount) {
@@ -89,7 +89,7 @@ func TestConnQueryValues(t *testing.T) {
 	}
 
 	if rows.Err() != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	if rowCount != 10 {
@@ -107,7 +107,7 @@ func TestConnQueryCloseEarly(t *testing.T) {
 	// Immediately close query without reading any rows
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 	rows.Close()
 
@@ -116,7 +116,7 @@ func TestConnQueryCloseEarly(t *testing.T) {
 	// Read partial response then close
 	rows, err = conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	ok := rows.Next()
@@ -145,7 +145,7 @@ func TestConnQueryReadWrongTypeError(t *testing.T) {
 	// Read a single value incorrectly
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	rowsRead := 0
@@ -181,7 +181,7 @@ func TestConnQueryReadTooManyValues(t *testing.T) {
 	// Read too many values
 	rows, err := conn.Query("select generate_series(1,$1)", 10)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	rowsRead := 0
@@ -211,7 +211,7 @@ func TestConnQueryScanner(t *testing.T) {
 
 	rows, err := conn.Query("select null::int8, 1::int8")
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	ok := rows.Next()
@@ -222,7 +222,7 @@ func TestConnQueryScanner(t *testing.T) {
 	var n, m pgx.NullInt64
 	err = rows.Scan(&n, &m)
 	if err != nil {
-		t.Fatalf("rows.Scan failed: ", err)
+		t.Fatalf("rows.Scan failed: %v", err)
 	}
 	rows.Close()
 
@@ -282,7 +282,7 @@ func TestConnQueryEncoder(t *testing.T) {
 
 	rows, err := conn.Query("select $1::int8", &n)
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	ok := rows.Next()
@@ -293,7 +293,7 @@ func TestConnQueryEncoder(t *testing.T) {
 	var m pgx.NullInt64
 	err = rows.Scan(&m)
 	if err != nil {
-		t.Fatalf("rows.Scan failed: ", err)
+		t.Fatalf("rows.Scan failed: %v", err)
 	}
 	rows.Close()
 
@@ -856,15 +856,15 @@ func TestReadingValueAfterEmptyArray(t *testing.T) {
 	var b int32
 	err := conn.QueryRow("select '{}'::text[], 42::integer").Scan(&a, &b)
 	if err != nil {
-		t.Fatalf("conn.QueryRow failed: ", err)
+		t.Fatalf("conn.QueryRow failed: %v", err)
 	}
 
 	if len(a) != 0 {
-		t.Errorf("Expected 'a' to have length 0, but it was: ", len(a))
+		t.Errorf("Expected 'a' to have length 0, but it was: %d", len(a))
 	}
 
 	if b != 42 {
-		t.Errorf("Expected 'b' to 42, but it was: ", b)
+		t.Errorf("Expected 'b' to 42, but it was: %d", b)
 	}
 }
 
@@ -875,7 +875,7 @@ func TestReadingNullByteArray(t *testing.T) {
 	var a []byte
 	err := conn.QueryRow("select null::text").Scan(&a)
 	if err != nil {
-		t.Fatalf("conn.QueryRow failed: ", err)
+		t.Fatalf("conn.QueryRow failed: %v", err)
 	}
 
 	if a != nil {
@@ -889,7 +889,7 @@ func TestReadingNullByteArrays(t *testing.T) {
 
 	rows, err := conn.Query("select null::text union all select null::text")
 	if err != nil {
-		t.Fatalf("conn.Query failed: ", err)
+		t.Fatalf("conn.Query failed: %v", err)
 	}
 
 	count := 0
@@ -897,14 +897,14 @@ func TestReadingNullByteArrays(t *testing.T) {
 		count++
 		var a []byte
 		if err := rows.Scan(&a); err != nil {
-			t.Fatalf("failed to scan row", err)
+			t.Fatalf("failed to scan row: %v", err)
 		}
 		if a != nil {
 			t.Errorf("Expected 'a' to be nil, but it was: %v", a)
 		}
 	}
 	if count != 2 {
-		t.Errorf("Expected to read 2 rows, read: ", count)
+		t.Errorf("Expected to read 2 rows, read: %d", count)
 	}
 }